How do i make my grounded variable change as I hit the platform and as I jump?

The Trigger entry and exits arent working and the boolean stays as false

using System.Collections; using UnityEngine;

public class CarMovement : MonoBehaviour { public float speed; public bool grounded = false; public float reverse;

 void Update () {

     if (Input.GetKey (KeyCode.RightArrow)) {
         if (grounded = true) {

             float moveHorizontal = Input.GetAxis ("Horizontal");
             Vector2 movement = new Vector2 (moveHorizontal, 0.0f);
             GetComponent<Rigidbody2D> ().AddForce (movement * speed);

         } 
         else if (grounded = false)
         {
             
         }
     }
     if (Input.GetKey (KeyCode.LeftArrow)) {
         if (grounded = true) {

             float moveHorizontal = Input.GetAxis ("Horizontal");
             Vector2 movement = new Vector2 (moveHorizontal, 0.0f);
             GetComponent<Rigidbody2D> ().AddForce (movement * reverse);
 
         }
     }
 }

 void OnTriggerEntry2D () {
     grounded = true;
     }

 void OnTriggerExit2D () {
     grounded = false;
 }

}