i cant do tha when the counter arrive to 19 in the liquid display errase the 2d

i cant do tha when the counter arrive to 19 in the liquid display errase the 2d number here is the program:

// include the library code:
#include <LiquidCrystal.h>

// initialize the library by associating any needed LCD interface pin
// with the arduino pin number it is connected to
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;

LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

int inicio = 0 ;
int reset = 0 ;
int seg = 1;
int minu = 1;
int hora = 0;

void setup() {
// set up the LCD’s number of columns and rows:
pinMode(6 ,INPUT);
}

void loop() {
inicio=digitalRead(6);
reset=digitalRead(7);

if( inicio == HIGH){
lcd.setCursor(4, 1);
lcd.print(seg++);
delay(500);
if(seg==19){
seg=reset;
lcd.setCursor(2, 1);
lcd.print(minu++);
if(minu==20){
minu=0;
lcd.setCursor(2, 1);
lcd.print(hora++);
}
}

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