Lip fibroma, common with some fish, angels seem to be one of them. A separate tank for healing afterward will need to be set up, a 10 gallon should work fine. You'll be doing daily 50% water changes on this tank for the first week, every other day for the second week, so unless you want to do this on a larger tank a smaller one makes life easier.
Get a wet towel to hold the fish, and a sharp single edged razor blade or exacto knife. Carefully cut off the firbroma, trying to remove the fibroma, but not any lip tissue. Don't leave the fish out of the tank longer than about a minute.
The clean water with the large frequent water changes will help with healing as well as the prevention of infection. A longish topic on lip fibromas in angels can be found
here.