Constantly Read Sensor Help!

I need help with my code. I am currently working on a simulation for a ventilator. I am working with Millis to constantly read my sensor, but I am doing something wrong. This is what I have for the code.
I need it to constantly read the sensor so it can execute the loop correctly.

Any inputs or ideas, please?

#include <Stepper.h>
#include <LiquidCrystal.h>

LiquidCrystal lcd (8, 9, 10, 11, 12, 13);


int enablePin = 7; //PWM2 which is B 1st cable Yellow
int in1Pin = A0; //2nd cable Green cable
int in2Pin = A1; //Brown cable
int enablePin2 = A3; //PWM1 which is A Purple Cable
int analogInPin = A4; //potentiometer
int sensorValue = 0;
int outputValue = 0;
//int state = 0;
//Following are for the sensors
int triggerPin = 6;//Sensor A (Bottom)
int echoPin = 5;//Sensor A (Bottom)
int echoPin2 = 4;//Second Sensor Top(B Sensor)
int triggerPin2 = 3; //Second Sensor Top(B Sensor)
int cm, cm1;

int buzzer = A5;
int light = 2;

Stepper stepper1(200, in1Pin, in2Pin); //200 is full revolution
const long eventTime_1 = 1000;
//const long eventTime_2 = 2000;
unsigned long previousTime_1 = 0;
//unsigned long previousTime_2 = 0;
unsigned long currentTime = 0;
/*---------------------------------------*/
//Toggles the input from the trigger to the echo pin
long readSensorA(int triggerPin, int echoPin)
{
  pinMode(triggerPin, OUTPUT);
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(2);

  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);
  pinMode(echoPin, INPUT);

  return pulseIn(echoPin, HIGH);
}
long readSensorB(int triggerPin2, int echoPin2)
{
  pinMode(triggerPin2, OUTPUT);
  digitalWrite(triggerPin2, LOW);
  delayMicroseconds(2);

  digitalWrite(triggerPin2, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin2, LOW);
  pinMode(echoPin2, INPUT);

  return pulseIn(echoPin2, HIGH);
}
/*------------------------------------*/

/*/////VOID SETUP//////*/
void setup()
{
  lcd.begin(16,2);
  Serial.begin(96000);
  Serial.println("------------");
  //lcd.begin(16,2);

  pinMode(in1Pin, OUTPUT);
  pinMode(in2Pin, OUTPUT);
  pinMode(enablePin, OUTPUT);
  pinMode(enablePin2, OUTPUT);
  pinMode(analogInPin, INPUT); //potentiometer
  pinMode(light, OUTPUT);


  digitalWrite(enablePin, HIGH);
  digitalWrite(enablePin2, HIGH);
  stepper1.setSpeed(100);
  

}

/*------------------------------------*/

/*/////VOID LOOP//////*/
void loop()
{
  //Comparing difference between current time and previous time in 1 sec
  //currentTime is always updating
currentTime = millis();
if(currentTime - previousTime_1 >= eventTime_1)
{
  readSensorA(6,5);
  readSensorB(3,4);
  previousTime_1 = currentTime;
}
  checkSensor();
  spinMotor();
  sensorLOW();
  sensorHIGH();
}
void checkSensor(){  
  cm = (0.01723 * readSensorA(6,5));  //(3,2) is for trigger pin, echo pin
  cm1 = 0.01723 * readSensorB(3,4);  //(3,2) is for trigger pin, echo pin
  sensorValue = analogRead(analogInPin);
  outputValue = map(sensorValue, 0, 1024, 250, 751);
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print(outputValue);
  lcd.print("mL");
  lcd.setCursor(0,1);
  Serial.print("Sensor A: ");
  Serial.print(cm);
  Serial.print("cm ");
  Serial.println();
  delay(10);
  
  
  Serial.print("Sensor B: ");
  Serial.print(cm1);
  Serial.print("cm ");
  Serial.println();
  delay(10);
  float AirSpeed=(0.3/2)*((cm/10000+cm1/10000)/(cm/10000*cm1/10000));

  Serial.print("Air flow =");
  Serial.print(AirSpeed);
  Serial.println(" m/s");
  Serial.println("-----------------------");
  delay(1000);
  previousTime_1 = currentTime;
}
}

void spinMotor(){ 

  if (sensorValue>outputValue)
  {
  // Turn the stepper 100 steps which means 180 degrees
  stepper1.step(100);
  // Wait half second
  delay(100);
  }
  
  if (sensorValue<outputValue){
  // Turn the stepper 100 steps back which means 180 degrees
  stepper1.step(-100);
  // Wait half second
  delay(100);
  }
  sensorValue=outputValue;
  
}

void sensorLOW()
{ 
  
    if ((0.01723 * readSensorA(6, 5) < 105) && (0.01723 * readSensorB(3, 4) < 105))
    {
  
   	lcd.print("Breathe:");
    	delay(1000);
    	lcd.setCursor(0,1);
    	lcd.print("Inhale 2 sec");
    	delay(1000);
    	lcd.setCursor(0,1);
    	lcd.print("Inhale 3 sec");
    	delay(1000);
    	lcd.setCursor(0,1);
    	lcd.print("Inhale 4 sec");
    	delay(1000);
  
    	lcd.setCursor(0,1);
    	lcd.print("Hold:         ");
    	delay(1000);
    	lcd.setCursor(0,1);
    	lcd.print("Exhale 4 sec");
    	delay(1000);
    	lcd.setCursor(0,1);
    	lcd.print("Exhale 5 sec");
    	delay(1000);
    	lcd.setCursor(0,1);
    	lcd.print("Exhale 6 sec");
    	delay(1000);
    }
    
  
}

void sensorHIGH()
{ 
  if ((0.01723 * readSensorA(6, 5) > 105) && (0.01723 * readSensorB(3, 4) > 105))
      {
      
    
        digitalWrite(light, HIGH);
        tone(buzzer, 659,1500);
        lcd.clear();
        lcd.setCursor(0,0);
        lcd.print("ERROR:");
        lcd.setCursor(0,1);
        lcd.print("No Airflow!!");
        delay(2000);
      } 
  
    else {
    
      digitalWrite(buzzer, LOW);
      digitalWrite(light, LOW);
      noTone(buzzer);
     
} 
}

You can't mix this sort of construct:

currentTime = millis();
if(currentTime - previousTime_1 >= eventTime_1)  // eventTime_1 = 1000 
{ . . . }

with this:

. . .
        delay(1000);
     lcd.setCursor(0,1);
     lcd.print("Inhale 2 sec");
     delay(1000);
. . .

The delay() statments will interfere with your timer.

But 2 general observations:

  1. You've created quite a lot of code and have not been able to give a very precise statement of what is going wrong. You should build such code incrementally in a way that you can test each part. Ideally, you would start off with a clear description of WHAT the code is intended to do, then begin to focus on HOW your code should achieve that.
  2. If you post code here, please use the automatic formatter in the IDE to correct the indentation. It is otherwise very difficult to read.