As per your suggestion I have made changes to my flow.
Now the issue is,
For the first time when I submit both the value for PM Name and PM email, it comes properly, however if 2nd time for the same Customer name if I change the PM name and keep the PM email blank, after the flow run, the PM name remains same (not getting updated) and the PM email field shows the Customer name.

Get Items:

length(outputs('Get_items')?['body/value'])


PM Name: Internal PM name is ‘field_6’
if(empty(outputs('Get_response_details')?['body/r8a05669fe13a4fc4a3f3f7cc3b69b9a5']),item()?['field_6'],outputs('Get_response_details')?['body/r8a05669fe13a4fc4a3f3f7cc3b69b9a5'])
PM email: Internal PM email is ‘field_8’
if(empty(outputs('Get_response_details')?['body/r50d6f4b60c104d3eb22ad3ce84afb33c']),item()?['field_8'],outputs('Get_response_details')?['body/r50d6f4b60c104d3eb22ad3ce84afb33c'])
For the first time when I submit both the value for PM Name and PM email, it comes properly, however if 2nd time for the same Customer name if I change the PM name and keep the PM email blank, after the flow run, the PM name remains same (not getting updated) and the PM email field shows the Customer name.

After flow run, the email field updated as Customer Name (Title)

Thanks
Varsha