Don’t use anything yet. If you try to use a charged tm it will fail so no real loss but the fast move isn’t important until after evolved. Anyway, just leave it alone until the next Team Rocket takeover event, then use a charged TM to remove Frustration. Then, if you want to you can use an elite charged tm to give him Earthpower after you evolve to Garchomp. Or, you can wait until December community day and you can use a regular charged tm to get that move.