you just can change reference to FollowGoal by any moment you want.
Transform FollowGoal;
Transform Enemy1;
Transform Enemy2;
void Update()
{
if(Input.GetKeyDow(KeyCode.1))
{
FollowGoal= Enemy1;
}
if(Input.GetKeyDow(KeyCode.2))
{
FollowGoal= Enemy2;
trasform }
Transform.position= Vector3.MoveTowards(transform.position, FollowGoal.position,speed);
}
```