https://docs.github.com/en/enterprise-server@3.7/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-base-branch-of-a-pull-request
Changing the base branch of a pull request - GitHub Enterprise Server 3.7 Docs
After a pull request is opened, you can change the base branch to compare the changes in the pull request against a different branch.
changing the basepull requestgithub enterprisebranchserver