This condition is called
Angina Bullosa Haemorrhagica (Oral
Blood Blister)
Caused by minor trauma like cheek biting , hot and spicy food , deficiency of vit
b12 and vit C.
Normally doesn't require any treatment its self limiting but if causing problem then can take vit 12 and vit c supplements , can use chlorhexidine mouth wash.
Drink plenty of water.
Avoid alcohol , tobacco , spicy food