Move humanoid body parts at runtime?

As I have to move the humanoid body parts at runtime, I thought that it could to be done by using a script. So I wrote a script that would do so. But when I run the project, the script doesn't function as it is intended to. For example if I need to rotate the leg backwards by 90 degrees, the script is unable to do so, it just rotates the leg in any direction. Are there any corrections I need to do? Or is there any other alternative? Please help.. The script is as follows:

 public class rayhit : MonoBehaviour {
 
     RaycastHit hit;
     Vector3 startPos1, endPos1;
     public GameObject isActive;
     public float speed;
     public Ray ray;
     public Rigidbody rigidBody;
     Vector3 targetPoint;
     bool Action = false;
     public float speed1 = 1.0F;
     private float startTime1;
     private float journeyLength1;
     // Use this for initialization
     void Start () 
     {
 
     }
     
     // Update is called once per frame
     void Update () {
         if (Action)
         {
             float distCovered = (Time.time - startTime1) * speed1;
             float fracJourney = distCovered / journeyLength1;
             //isActive.GetComponent<Rigidbody>().position = Vector3.Lerp(startPos1, endPos1, fracJourney);
             //isActive.transform. = Vector3.Lerp(startPos1, endPos1, fracJourney);
             Vector3 targetDir = endPos1 - isActive.transform.position;
             Vector3 forward = isActive.transform.forward;
             float angle = Vector3.Angle(targetDir, forward);
             print(angle);
             isActive.transform.Rotate(Vector3.up * Time.deltaTime*5,angle, Space.World);
             Action = false;
         }
     }
     void FixedUpdate()
     {
         if (Input.GetMouseButtonDown(0))
         {
             var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
             //Debug.Log("mousse");
             
             print(ray);
             if (Physics.Raycast(ray, out hit))
             {
                 if (hit.rigidbody != null)
                 {
                     Debug.Log("Hit = " + hit.collider.gameObject.name);
                     isActive = hit.collider.gameObject;
                     isActive.transform.rotation = new Quaternion(0,0,0,0);
                     //isActive.GetComponent<Rigidbody>().constraints = RigidbodyConstraints.FreezeRotation;
                     startPos1 = isActive.transform.position;
                 }
             }
             else
             {
                 print("Else");
                 ChangeRotationTarget();
                 Action = true;
             }
         }
     }
     void ChangeRotationTarget()
     {
 
         Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         Plane playerPlane = new Plane(Vector3.up, transform.position);
 
         float hitdist = 0.0f;
 
         if (playerPlane.Raycast(ray, out hitdist))
         {
             targetPoint = ray.GetPoint(hitdist);
         }
         endPos1 = targetPoint;
         print("Target:"+targetPoint);
         startTime1 = Time.time;
         journeyLength1 = Vector3.Distance(startPos1, endPos1);
         print("Distance" + journeyLength1);
 
     }
 }