I Highly recomend you don't do this, but If you dare, erase the pencil marks with an eraser (v1-v4.5 ((American only)) To undebug v5, try taking the wire off that you soldered on.
If I were you, I wouldn't debug a Tamagotchi. You are risking the chance of breaking it. I don't know because I play it safe and don't even try to debug anything.