So I want to login to Facebook with my currently ML profile but my Facebook account already got a ML profile.

Question: how do I get rid of the ML profile already on my Facebook acc? Cause I want to sign in my currently ML profile to Facebook.

Once an account is linked to FB, you cannot remove it, sorry.

Sorry to say but once a ML profile is connected to a Facebook account, you won't be able to disconnect it.
If you want to connect your current ML profile to Facebook, it'll have to be connected to a new Facebook account instead