I forgot a small change in the initial git commit of a new project. I didn’t want to have an extra commit for a little fix like that, so I tried combining it.

I found a Stack Overflow post telling me what to do— in TortoiseGit Log, select the two commits, right-click and Combine.

These were the first two commits to a new repository, though, so it popped up a message: “The following commit dialog can only show changes of oldest commit if it has exactly one parent. This is not the case right now.” Indeed, the Commit dialog that popped up showed only the second revision’s change.

I edited the commit message (which consisted of both revisions' messages) and committed. And hooray, I then had only one commit.