Just in case you know something I don’t, this is what happens when I try to manage Matter in the Aqara app.
If I hit bind, it takes me through the M3 Hub setup wizard.
EDIT:
I’m an idiot. 
I added the lock via Apple Home, so I was able to find “Connected Services” there and removed the numbers related to my Homey Pro. Now I’ve successfully added the lock again.
