accelstepper continuous rotation with forward and backward control

Question

I am using Uno and the A4988 driver with nema17 motor and finally the Accelstepper, I want to make the motor run endlessly in a direction, but when I press a button I want it to stop and run in the other direction also endlessly until I push the button again, here is my code:

// Include the AccelStepper Library
#include <AccelStepper.h>

// Define pin connections
const int dirPin = 2;
const int stepPin = 3;
const int dirButton = 8;
int potPin = 0;

int buttonState = 0;

// Define motor interface type
#define motorInterfaceType 1

// Creates an instance
AccelStepper myStepper(motorInterfaceType, stepPin, dirPin);

void setup() {
  pinMode(dirPin, OUTPUT);
  pinMode(dirButton, INPUT_PULLUP);
  myStepper.setMaxSpeed(500);
  Serial.begin(9600);
}

void loop() {
  int speed = analogRead(potPin)/4;
  myStepper.setSpeed(speed);
  digitalWrite(dirPin,LOW);
  buttonState = digitalRead(dirButton);
  
  if(buttonState = 0){
    
  }
  
  Serial.print(buttonState);
  delay(5);
  myStepper.run();
}

so the question is what should i put inside the :

if(buttonState = 0){
        
}

to make it switch direction?

I tried countless examples from the internet but the motor never changes direction.

thanks