To combine the excellent advice in this thread, all of which I had to follow to get this to work in Xcode 13:
Select Enable Code Review
Select side-by-side comparison from Adjust Editor Options
(the center button with horizontal lines in the image below)
Find the comparison arrow
at the bottom right of the content window,
Select the branch and commit hash you'd like to revert
on the right hand side of the code review selection arrows. (If your project has a large history, it may take some time for the commit hash list to populate.)
Choose Local Changes / Uncommitted Changes
on the left hand side of the code review selection arrows. This may be already selected, but you may need to reselect Local Changes if you've been mucking about with options for awhile.
Correctness check:
Your commit selection area should now look something like this:
Find the change and discard it
Now scroll to a change and click the blue bar in the gutter of the left-side editor. This will reveal the "Discard Change" action you've been dreaming of!
Topic:
Developer Tools & Services
SubTopic:
Xcode
Tags: