I'm making a note of this so I'll remember how to do it next time:
- Select the file you want to roll back. Right-click, select "Graph selection" (or hit Ctrl+G)
- Right-click on revision you want to remove. Select "Admin options > Delete revisions"
- Click around to get out of graph view. You'll notice the file is still at the wrong version. Right-click on the file, select "Update," check "Get the clean copy," and it will revert back to the correct version.
I tried the command-line options I found via a Google search, but that just generated weird syntax errors in CVS. This way actually worked.