Reverting commit
This issue shows how to revert commits so as to solve the specific problem of helping @julia.longtin revert the last commit using only the gitlab web interface (and not using the command line, which she is comfortable and familiar with).
Step 1: Get to latest commit (one way to do this is under Project Overview -> Activity
Step 2: From the commit page, select Options -> Revert and it will allow you to create a new commit reverting the last commit.