Admitadely I am a little confused, so might be my response is a little out of place, but
after some careful deducing I assume you all are talking about how to change a move before sumbitting it (when submit mode is turned on). In which case just clicking elsewhere changes it…
But just to entertain the possibility or help those who find this thread after looking for a simple undo after misclicking (and single click submit mode is on) the button is here: (may be labeled differently based on your language settings)
Your opponent has to accept such an undo (because it is your fault so to say), so if it’s a correspondence you have to wait until he logs on, or it may be declined alltogether. It is also probably a good practice to apologize/explain in chat.