Inverted gravity makes character walk on the wrong side of the platform

I am very new to Unity and have got a scene that I am supposed to change. I'm trying to make a game like gravity guy, but whenever I try to change back to "regular" gravity, my character starts walking on top of the "top floor" instead of moving back down... I found a couple of solutions on the internet that I could not get to work. Any advice would be appreciated.

 public Vector3 jump;
 public float jumpForce = 2.0f;
 public float jumpSpeed = 1.0f;
 private Vector3 moveDirection = Vector3.zero;


 public bool isGrounded;
 Rigidbody rb;
     


 // Use this for initialization
 void Start()
 {
         rb = GetComponent<Rigidbody>();
         jump = new Vector3(0.0f, 2.0f, 0.0f);
     

     // get the third person character ( this should never be null due to require component )
     character = GetComponent<ThirdPersonCharacter>();

     StartCoroutine(Choreography());
 }

 // Update is called once per frame
 void Update()
 {

     if (Input.GetKeyDown("down"))
         Physics.gravity *= -1;
 
 
     if (Input.GetKeyDown("down"))
         transform.Rotate (transform.rotation.x,transform.rotation.y,transform.rotation.z-180);

     if (Input.GetKeyDown("down"))
         moveDirection.y = -jumpSpeed;


 }



 void OnCollisionStay()
 {
     isGrounded = true;
 }

 IEnumerator Choreography()
 {
     yield return new WaitForFixedUpdate ();


     //walk forward
     float startTime = Time.time;
     float duration = 120f;
     while (Time.time < startTime + duration) {
         character.Move (Vector3.forward, false, false);
         yield return new WaitForFixedUpdate ();
     }
 }