Work in a tray or over a table top so as to not loose the screws. Alternatively get a strong magnet with which to sweep the floor, they are very handy.
The problem you face is that getting a replacement yaw arm may be difficult. I can't find one at the moment on the www, I found a zoom arm but I doubt they are the same. Also the roll and yaw motors are built into the arm. Have a look at the following video around the 21 minute mark
.
I have stripped a knackered
M2P gimbal and couldn't see a way of removing the motors from the yaw arm.
Working with them is fiddly, very fiddly, in places but providing you have the correct screwdrivers and keep your cool it is not difficult.
A replacement arm with motors may need calibrating, have a look at
Mavic 2 gimbal repair and calibration
The procedure with python looks fairly routine but I have not gone through the calibration video to see how well it worked.
I suggest you post photos of the arm so that we can see how bent it is. It might be straightenable if you have the tools but that is not guaranteed, not even in the slightest and it may snap.
I would also suggest you strip the gimbal and look for damage to travel limiting stops, you'd need to work out what acts as the stops as you dismantle the gimbal. From memory the pitch limiters are a projection or projections on the bearing insert and corresponding slot/s but I can not remember what the roll and yaw limiters were.
Though thinking about the yaw I'd be inclined to check whether or not screws have been pulled through the plastic of the gimbal carrier, (the thing with rubber dampers on and the gold coloured cap.)
As to whether to send it to a repairer or DJI themselves, hmmmmm, you pays your money and takes your choice. With DJI I imagine you will get a replacement drone rather than them actually repairing your drone, they probably repair the damaged drone later and at their convenience. A repairer may have to actually repair the gimbal.
However
BEFORE ANY OF THIS HAPPENS I would suggest you find out WHY the drone fell from the air in the first place.
Have a look at the instructions for retrieving logs on the following page,
DJI Flight Log Viewer | Phantom Help
Upload the log to that page and then post, here, the resulting link. If your controller is an RC1A there should, in the folder where you found the txt flight log, another folder whose name starts "MCDat". In that 2nd folder you should find a corresponding DAT flight log. It might be useful to post that too but post that here, not via Phantomhelp.