No power?

Connect the jump box and push the trunk button in the driver's side footwell. If the lock has power, it should open. I would also try connecting a charger to the jump point and see if you can get the battery to charge at all. Being a repo it's going to be difficult as you don't know what the previous owner may have done to it. Then you will likely need a locksmith or dealer to program the fob back into the system, if you have the correct one. BMWs do some odd things when they lose power.

That is not a good sign water in any of the modules that are network connected can cause a lot of unexpected things to happen. In this case the FEM also controls the rear power module in terms of it powering on properly. Take a test light and see if you are showing power on fuse 11 in the FEM. If not, you might try using the jump box and applying power to the circuit with the fuse out and see if it powers the rear module on enough that you can at least get the trunk to open and maybe if it powers up it will let you shift into park.

If the fuse is good, does it have power? That one should power on with the push to start. The problem is that most of the power circuits for the system are in the rear.

Okay, then the rear box should be waking up. The rear trunk release under the trim does nothing either. The interior and exterior use slightly different paths to release the latch but then you still have the lift motors to deal with. I don't see any good way to get the trunk released without having full power to the vehicle. I sort of wonder if someone didn't pull a couple fuses in the rear box and then slam the trunk. The neutral lockout it's in should have automatically released as soon as the start button was touched to turn things off. It also should have returned to park as soon as you touched the button when you applied power, but if a fuse was missing so the power to that system was out nothing would respond.
I know on some of the earlier ones you could remove the plate lights and go in though there and release the trunk latch and on some you can drop the center section of the rear seat and crawl in that way to access the emergency release, or use a hook to pull it so you don't need to crawl in. Then you could check the electrical system fully.

Depends on the fuse, wouldn't take much to lock you out of the trunk and shut down the starting system.

Okay, go under it, look on the side of the transmission for a hex bolt in the flange of the case at the pan. That bolt pushes the release and locks out park. Remove the bolt and you should get control back.

You are welcome.