Well, it is always up to your consideration, it is nice to grant an undo if you feel your opponent just sincerely misclicked as it keeps the game even and “warm” but there certainly is no obligation whatsoever.
If you do not want to (I get that feeling from your question), don’t. Submit button is default settings for correspondence so miscklicks should not be that common.
While I haven’t done so in a tourney, I have accidentally mis-clicked, but only on a phone. I went to zoom out to hit submit, but my thumb moved my stone just before my finger hit the submit button. Probably not a constructive input, but I just wanted to throw my experience with that in the mix.