I just helped a new contributor land their first PR and we made a typo in the bpo number. I discovered this after the commits were merged upstream in the master, 3.8, and 3.7 branches.
It’s a very minor doc fix. Should I try to somehow redo those commits, or just let it slide?
I would say that, if the PR added a NEWS blurb file with the wrong bpo number, that should probably be fixed since it will show up incorrectly in the published docset changelog. To do so before the fix has been integrated into a release requires renaming the blurb file in Misc/NEWS.d/ in all branches it was merged to. If the PR has already been merged and released, then the Misc/NEWS.d/3.x.x.rst file should be edited as needed in each branch merged. I wouldn’t worry about fixing the git commit message.