When your repositories have PR with a lot of commits, you might want to select and apply only several commits out of them, git-cherry-pick is what you’re likely to use.
Here the steps taken during cherry-pick:
$ git log --oneline
$ git checkout -b save-master master
$ git pull FORK_GIT_URL master
$ git checkout master
$ git cherry-pick HASH_ID
...
$ git log --oneline
$ git push origin master
$ git branch -D save-master
Above commands are self-explanatory enough for you I guess. You can cherry-pick any commit you want to merge. If there is any problem during cherry-pick, you can just stop and restart cherry-pick again.
$ git cherry-pick --abort
or
$ git reset
This is applied to all popular Git servers, including GitHub, BitBucket and GitLab.