As per I know once your app is in production, you cannot change anything.
You need to ask the developer support team for any help by submitting a support ticket. Once they added the permission with your request(not sure if they do.. most probably they don't) you need to test again for that permission you acquired.
The official recommendation is to create a new app, add proper permissions and graduate it. So in that case you need to go through again.
Using the RingCentral Phone for Desktop, you can dial or receive test calls, send and receive test SMS or Fax messages in your sandbox environment.
Download RingCentral Phone for Desktop:
Tip: switch to the "sandbox mode" before logging in the app:
2 People are following this question.