You will have to reverse all logic.
void Sensor_Trigger()
{
bool isWithin57 = false;
for (int sonarCnt = 0; sonarCnt < SONAR_NUM; sonarCnt++)
{
if (sonar[sonarCnt].ping_cm() < 57)
{
isWithin57 = true;
}
}
// if any of the sensors sensor measures less than 57
if (isWithin57 == true)
{
Motor_Driver_1_RS.backward();
Serial.println("Motor Driver 1 L/S is ON - Forward");
delay(500);
Motor_Driver_1_RS.stop();
Serial.println("Motor Driver 1 L/S is OFF");
}
}