rotate object 0 to 90 with speed 1 then wait then 90 to 0 degree with 1 speed unity c#

i want to Rotate my object 0 to 90 degree with 1 speed --> then wait for 3 Sec ---> Then Rotate again 90 to 0 degree with 1 speed --> Then wait for 3 sec

i need above process in loop

i m success with it but it working only 1 time in Start Function

In update function its not working

below my Start Function code

 IEnumerator Start()
 {
     StartCoroutine( RotateMe1(Vector3.forward * 90f, 1f));
     yield return new WaitForSeconds(3);
     StartCoroutine(RotateMe2(Vector3.forward * 0f, 1f));
     yield return new WaitForSeconds(3);
 }
 
 IEnumerator RotateMe1(Vector3 byAngles1, float inTime1)
 {
     var fromAngle1 = transform.rotation;
     var toAngle1 = Quaternion.Euler(transform.eulerAngles + byAngles1);
     for (var t = 0f; t < 1; t += Time.deltaTime / inTime1)
     {
         transform.rotation = Quaternion.Lerp(fromAngle1, toAngle1, t);
         yield return null;
     }
 }
 
 IEnumerator RotateMe2(Vector3 byAngles2, float inTime2)
 {
     var fromAngle2 = transform.rotation;
     var toAngle2 = Quaternion.Euler(transform.eulerAngles + byAngles2);
     for (var t = 0f; t < 1; t += Time.deltaTime / inTime2)
     {
         transform.rotation = Quaternion.Lerp(fromAngle2, toAngle2, t);
         yield return null;
     }
 }

Below my Update Function code

 void Update()
 {
     StartCoroutine(RotateMe1(Vector3.forward * 90f, 1f));
     StartCoroutine(Wait());
     StartCoroutine(RotateMe2(Vector3.forward * 0f, 1f));
     StartCoroutine(Wait());
 }
 
 IEnumerator RotateMe1(Vector3 byAngles1, float inTime1)
 {
     var fromAngle1 = transform.rotation;
     var toAngle1 = Quaternion.Euler(transform.eulerAngles + byAngles1);
     for (var t = 0f; t < 1; t += Time.deltaTime / inTime1)
     {
         transform.rotation = Quaternion.Lerp(fromAngle1, toAngle1, t);
         yield return null;
     }
 }
 
 IEnumerator RotateMe2(Vector3 byAngles2, float inTime2)
 {
     var fromAngle2 = transform.rotation;
     var toAngle2 = Quaternion.Euler(transform.eulerAngles + byAngles2);
     for (var t = 0f; t < 1; t += Time.deltaTime / inTime2)
     {
         transform.rotation = Quaternion.Lerp(fromAngle2, toAngle2, t);
         yield return null;
     }
 }
 
 IEnumerator Wait()
 {
     yield return new WaitForSeconds(3);
 }

Here i recorded Video for issue of Update Function

i attached above script on AXE in attached above Video

PLease help me