If you’ve ever owned a Baume et Mercier Hampton, I am sorry. You bought a lemon. The watch was a profit center and not much else. The smallest of all quartz movements, coupled with the worst case back in recent history, all leading to a town called Trouble.
They even got people to swipe their cards for the 18k gold models, the biggest of shams. If you have one, bail and trade out if possible. Most hacks will ruin the back trying to replace the first battery (it requires a special tool). If they do manage to get the watch open, it is then passed around to laugh at the movement. No surprise that it’s just as much as of hassle trying to get the caseback snapped on again (tip: it goes one side at a time with a small ridge to start out the first side).
Baume never intended this watch to be opened by anyone but their service center, I am sure. Steer clear of this timepiece on forums and with trades. I know this did not help you.