You've submitted a pull request against the Elgg repo and core members have asked you to make some changes. (PR = pull request from here on)

Check out your work branch in case you've been working on something else in your local repo:

cd ~/htdocs/elgg18
git checkout my-branch-name

Make your changes as necessary, test and commit them. Your later commit messages don't necessarily need to include the ticket number.

To update your PR, just re-push to your github repo:

git push fork my-branch-name

You'll see the additional commits at the bottom of your PR. If you think necessary, add a brief note to the PR describing the changes.

That's it!