How to remove custom domain from all projects?

I recently tried custom domain for github pages. Now I am not able to remove domain from the projects. The old domain is not available to me anymore. I need help on how to get back to

Delete the CNAME file from the repository to revert back.

There are no CNAME files. All the repository github pages are redirected to another domain. Instead I tried to create an empty CNAME file. but that didn’t work either.

Your repository still has a CNAME file, delete it and things will revert back.