My pull request was successfully merged, however my forked repository is still showing that 5 commits are ahead, after those commits were merged in my PR.

Any idea on how to get everything equalized again? This can be a problem for future pull requests where the past commits show up in the pull request.

Tried: various commands from other similar questions on stackoverflow, such as:

git fetch --all
git push --force upstream/master:master
git push --force
git fetch upstream

Any commands with upstream shows UPSTREAM as an unknown repository.

fatal: 'upstream/master:master' does not appear to be a git repository
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Expected: everything to equalize, between the forked repo and the original repository.
Actually resulted: Nothing happened to any repository from what I could tell.