If there's a conflict, Retcon shows that to you, but you can keep freely moving commits around—it's not blocking.
Once you're happy with how your history looks like, you can start actually resolving any remaining conflicts, and after that the history gets actually written.
Sometimes, just moving things around further is enough to resolve the conflicts, too, if they're simple enough!
Sometimes, just moving things around further is enough to resolve the conflicts, too, if they're simple enough!