Easily done with a file. Must be done in a bench vice. Pull the bolt into the "cocked" position and hold it open with something so you don't accidentally file the sear engagement, and continue the existing flat to the back of the bolt body. In the same setup, use a small very very fine knife sharpening stone to carefully polish the sear engagement surface, making sure it stays perfectly flat. Dremel tools will absolutely #### this up. Tiny polishing stones are easily bought on any of the cheap import sites like AliExpress for the knockoff edgepro systems, should only cost 3 or 4 bucks. Even if you're going slow shouldn't take you more than an hour.