Smooth Rotation?

In my Skript The Player Rotate Towards the touch position:

var dir = touchPosition - Camera.main.WorldToScreenPoint(transform.position);
var angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
transform.rotation = Quaternion.AngleAxis(angle, Vector3.forward);

What have I to do, that the player Rotate Smooth?

You can use Mathf.Atan2() to derive the correct heading from where you are to where you want to look.

Then instead of just setting the rotation, you could use Mathf.DeltaAngle() to decide which way to smoothly tween your current heading to face the new direction.