I would you like to process at the moment when press Buttons

Hey everyone,
I created a System. This System has got Step Motor and Led. I added buttons with Processing on System but I want to use together all Buttons on System. My problem is here. I am pressing button. It is working. Okay! but I pressed other Buttons but not working at the moment. Other buttons are waiting end of process. I added look like “START” and “STOP” Buttons. If I pressed “START” button, I can’t stop processing. I must wait end of the process. I don’t want to wait. I would you like to process at the moment when press Buttons. I need help for this topic. What should I do? I hope so You can help me. I am sharing codes under this topic. Thanks for reading…
ARDUINO CODES>

int dirPin = 2;
int stepPin = 3;
int ledPin = 4;
int incomingByte = 0;
int stepsPerRevolution = 400;

void setup() {

  pinMode(stepPin, OUTPUT);
  pinMode(dirPin, OUTPUT);
  pinMode(ledPin, OUTPUT);

  Serial.begin(9600);
  Serial.println("Press 7 to ↓50");
  Serial.println("Press 6 to ↑50");
  Serial.println("Press 5 to GO HOME");
  Serial.println("Press 4 to LED OFF");
  Serial.println("Press 3 to LED ON");
  Serial.println("Press 2 to StepMotor STOP");
  Serial.println("Press 1 to StepMotor >");
  Serial.println("Press 0 to StepMotor <");
}

void loop() {
      if (Serial.available() > 0) {
       }
        incomingByte = Serial.read();
              
              if(incomingByte == '7'){

            digitalWrite(dirPin, LOW);
          
            for (int i = 0; i < 0.5*stepsPerRevolution; i++) {
              
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(0);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(0);
    
            Serial.println("↑50");
            }
       }else if(incomingByte == '6'){

            digitalWrite(dirPin, HIGH);
          
            for (int i = 0; i < 0.5*stepsPerRevolution; i++) {
              
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(0);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(0);
    
            Serial.println("↑50");
            }
       }else if(incomingByte == '5'){
           
            digitalWrite(dirPin, LOW);
          
            for (int i = 0; i < 4*stepsPerRevolution; i++) {
              
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(0);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(0);
    
           Serial.println("GO HOME");
                   incomingByte = Serial.read();
        }
        }else if(incomingByte == '4'){
           digitalWrite(ledPin, LOW);
           Serial.println("LED OFF");
        }
        if(incomingByte == '3'){
           digitalWrite(ledPin, HIGH);
           Serial.println("LED ON");
        }
        if(incomingByte == '2'){
           Serial.end();
           Serial.println("StepMotor STOP");
        }
        if(incomingByte == '1'){
            digitalWrite(dirPin, HIGH);
          
            for (int i = 0; i < 1*stepsPerRevolution; i++) {
              
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(0);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(0);
    
            Serial.println("StepMotor >");
        }

        }else if(incomingByte == '0'){

            digitalWrite(dirPin, LOW);
          
            for (int i = 0; i < 1*stepsPerRevolution; i++) {
              
    digitalWrite(stepPin, HIGH);
    delayMicroseconds(0);
    digitalWrite(stepPin, LOW);
    delayMicroseconds(0);
    
            Serial.println("StepMotor <");
            }
        }
        }