How to do a rebase with git gui?

Question

I know how to do a git rebase from the command line, but how do you do it with the official git-gui?

Answer 1

git gui can be used to add files to the index when doing a rebase --interactive (as mention in thegit rebase man page, The GitHub rebase help page or in this git rebase interactive tip article), but not to perform the rebase itself.
(unless, as you saw, you define the command yourself in the Tools section)