Regulating watches is not rocket science usually. I have only cracked open a few of my watches to make adjustments, but it is frequently fun and rewarding. My 5002 Big Pilot was a great success that I got down to a fraction of a second a day through trial and error. A loupe, case back tool, and watchmaking screwdrivers are all that’s needed. A timing device or app that listens to the watch tick is helpful.
Otherwise you are relying on a watchmaker that likely just wants to make sure not to adjust to a too slow rate.