Here's a KB article on how to customize RingOut numbers.
https://support.ringcentral.com/app/phone/desktop-web/enabling-using-ringout-ringcentral-app-desktop-web.html

Thanks Mary. It tells you how to add new RigOut numbers but not how to edit or delete existing numbers that you have already added. I'dbe grateful for help on that.

Not sure what you want to achieve exactly but one suggestion is:
Admin Portal > Users > click on a user > Outbound calls/faxes > caller ID
Here you can edit the default number used for RingOut.
Additionally you could remove the permission of a user to change his caller ID, so that you guarantee that the user extension uses the default caller ID you set there.
Is this what you want to achieve or is it something else?

Thank you for taking the time, but it was something else. I now have a solution - thank you.