Ask HN: Best way to claim username on Facebook and Instagram?
You can't even do that if you have legit trademarks.
Facebook just outright refuse to give the username. If it's used by another, what rights can be derived from the trademark? If the username you're claiming has been used since (long) time, than, there is no right for you. First come, first serve.. You have to talk to the account directly. After that, you'll need to find a way to transfer it from them to you.