Worse Wi-Fi Signal after drop. What I must to replace?

a few things can cause wifi signal disruption

if it was directly after a drop, it usually rules out software, unless there it caused a physical corruption in the memory banks. i like to start with a factory reset to rule out the failure. however, this will rmeove all personal files.

then go with a disassembly, and reassembly. fully pull apart the device, and reassemble it. There are plenty of pickups for the networks embedded into frame components, and one may have been dislodged.

Check for physical damage to components. (chips, cracks, pieces broken off of the board, etc) replace if needed.

i would go forward and try a coaxial cable replacement. there are black and white wires running up the sides of the device.

elsewise, the WiFi Addapteris integrated to the motherboard, and either you would need to SM Solder a new adapter onto the board, or replace the motherboard.