rotate 2d object toward movement

Hello all,

I'm building a simple 2d snake game and I'm trying to figure out how to move the "head" of the snake on Input without messing with the inputs directions

this is the script. It says that the snake first moves left and then according to the inputs. once I've tries changing rotation of the transform it didn't work and also Mathf.Atan2 didn't work for me...

I realize this is a very common question... Script:

 public class SnakePlayer : MonoBehaviour {
 
     Vector2 dir = Vector2.left;
 
     void Start ()
     {
         InvokeRepeating("MoveSnake", 0.6f, 0.6f);
     }
     
     void Update () {
         if (Input.GetKey(KeyCode.RightArrow))
         {
             dir = Vector2.right;
         }
         else if (Input.GetKey(KeyCode.DownArrow))
         {
             dir = -Vector2.up;
         }
         else if (Input.GetKey(KeyCode.LeftArrow))
         {
             dir = -Vector2.right;
         }
         else if (Input.GetKey(KeyCode.UpArrow))
         {
             dir = Vector2.up;
         }
 
         }
 
     void MoveSnake()
     {
         transform.Translate(dir);
     }
 
 }