Ladies and gentlemen, I here by announced: the fixing is successful!
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​After careful examination, I assume that the lower part of the grip was hit when it fell, and then the camera fell to the ground. At that time, the DX 16-50 lens was installed, which is short and light, and the mount should not be deformed. The only damaged part should be the frame around the battery compartment.
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​After the drop, the cover of the battery compartment can not close properly due to the frame deforming. And if you force it to close, not only it will be stuck, but there will also be bulges. ​So I took the pliers and put a paper towel on it to knock the deformed part back. Now the battery compartment cover is very flat when closed. I would say that's a big success!
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​Although the camera is a precision instrument, after all, the Nikon z502 does not have CMOS vibration reduction. I would be fairly confident to say that there are no moving parts inside the body, so I directly hammered the frame while not disassembling the whole machine. I have a wood chip pad underneath, which should absorb the most hit and shouldn't cause any further problems. I mean, economically speaking, it's Nikon Z502, not a Z8 or Z9. Sending it back to the factory for a full examination is not worth it.

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Also, a lesson learned: either mount the camera on to the tripod or hands on your neck. Do not let your hand hold it while not mounting anywhere.