Blister in mouth
The good news is that unless the blister is in a location where you often accidently bite it, it will heal in a few days.
A topical over the counter anesthetic
gel can be helpful to soothe pain and discomfort. Avoid food and drink that are temperature extremes, as well as those that are salty or spicy as they can be irritating to the blistered area.
If you have blisters often, see your dentist.