Current questions and answers regarding the map editor.

Hi! I recently started creating my own maps. And I have a question: how can I allow the player to choose a hero? (Maybe it's a silly question and it's already been asked, but the search didn't help). I suspect it's related to the Entry point, but I can't figure it out.
I also have a couple more questions.
Is there a button in the editor to undo the last action?