Thanks for writing to us.
Flaps of skin, more towards the back of the cheek are often caused by cheek bite. It could also be caused by the cusps of the molar teeth constantly rubbing your cheek.
My suggestion to you is that is not related to a canker sore
, You need to see a dentist
so that -
1)If the flap of skin has to be removed he can remove it
2)if corrective action needs to be taken regards teeth your teeth may need to be rounded off or any other treatment to correct you from biting the cheek may have to be done.