its a common fault and fix
see the 2 big screws at either side of the back- those go in to the bracket at the top of the mechanism, holding the top/bottom of the seat together, one of those has broken, and possibly a cable
the plastic covers- undo the big plastic screw in the center, and they pull/wiggle free and off, then remove the cable, and then undo the 2 big screws at the back, and lift the top half of the seat free, so it looks like the pic below, you can see the bracket at the top of the mechanism,this is one i replaced , i find/think its better to replace the whole mechanism for a decent one than mess about welding it, also you can still buy new cables if you need from bmw (these are what operate the tilt of the seat), and its also a good chance to give the mechanism a good clean and lube/oil etc and get it all looking and working good , its not hard to do a bit fiddly and trial and error but you figure it out, then once done its good practice to remove the passenger seat and just give the mechanisms a clean and lube up and oil the gas struts, and periodicly re-tighten the screws in the back
