Pushing commits to someone else's PR

gistfile1.txt

# Terminology
their_username = the GitHub username of the contributor who submitted the PR
their_branch = the name of the branch they used to submit the PR
repo_name = the name of your GitHub repository

# First add their fork as a remote
git remote add $their_username git@github.com:${their_username}/${repo_name}.git

# Then fetch it
git fetch $their_username

# Checkout the branch they used for the PR
git checkout $their_branch

# ... Make your changes and commit them ...
git commit -m "Minor fixes"

# Push to their branch
git push -u $their_username $their_branch

# You can even do things like rebase their branch against master and force-push.
# Probably best to warn the contributor before you do this though!
git rebase origin/master
git push -f