That sort of thing can be really vexing. Never dealt with it on this or any other amp, but I've wrestled with plenty of car trim that had similar issues. I guarantee hitting it with a hammer will only make the problem worse. The trim still won't lie flat, and it will have a new dent, too. My first step might be trying to glue it down with a low-adhesion glue like rubber cement. If that doesn't work, the glue can be cleaned off easily and you're only back to square one, not square negative one. But test it first on a portion of the grill cloth inside the amp to see whether it stains. Ultimately, with car trim, the answer almost always winds up being near-complete disassembly and reassembly from scratch, paying absolute attention to getting everything just exactly so. OTOH, as much as we love these little Pathfinders, they are just relatively inexpensive machinery. The simplest answer would be some heavy-duty glue, with full awareness that it might stain the cloth and it will complicate things if you ever need to take apart the baffle or replace the grill cloth in the future.