How to move an rigidbody left and right as it is moving up

I have a game object with a rigidbody. It is like a space which is continuously moving up and then when the player presses the left arrow, I want the object to shift left to avoid obstacles. I have been trying to use rigidbody.moveposition to do that but when ever i press the left button, the spaceship moves to left and stop moving up and then also disappear from the screen. How can I fix this so that when the user presses left, the spaceship moves smoothly to the left as it keeps moving up. This is the code that I used:

  public class PlayerController : MonoBehaviour {
                 Rigidbody2D rb;
                 public float gameSpeed;
                 bool moveLeft;
             

             // Use this for initialization
             void Start ()
             {
                 rb = GetComponent <Rigidbody2D> ();
             }
             
             // Update is called once per frame
             void Update ()
             {
                  if (Input.GetKeyUp (KeyCode.LeftArrow)) 
                 {
                     moveLeft = true;
                 }
             }
         
             void FixedUpdate ()
             {
                 MovePlayer ();
             }
         
             void MovePlayer ()
     {
         rb.velocity = (new Vector2 (0, 1f)) * gameSpeed; //Move player continuosly up
                 //Move Player to left and right as player keeps moving up.
         if (moveLeft) 
         {
             rb.MovePosition (new Vector2 ((transform.position.x - 1.4f), transform.position.y));
         }
     }