If the blister is painful then it can be canker sore and if the blister is painless then it can be mucocele. You can use topical ointments like numbing ointments, such as benzocaine (Oragel), anti-inflammatory (steroid) gels,benadryl allergy liquid mouthwash,oral preparations of steroids and vitamin supplements.
But if the sores last then mucocele need to be ruled out. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.