I have a blister on my gum above the tooth I had the crown put on (Photo)

The blister should be looked at by the dentist.  It could be an infection or may be there from before you had your root canal done.  There are several reasons it may be there.

Hello and thank you for your question. It’s difficult to tell from your pictures. I recommend following up with your Dentist or a Prosthodontist to make sure this is not an infection. A Prosthodontist is a dental specialist who has advanced training in tooth restoration.

Hi:Most likely the blister is abcess.  It’s best to go to your dentist right away for an X-ray and clinical evaluation.Best,Dr. Maddahi

From your photo it appears that you have an infection in the tooth. You stated that a root canal was done before the crown. You need to seek out a dentist and have a new X-ray taken to try and find the source of your infection. It is possible that the root canal may need to be retreated