Hi @gordonzhou
Here's a [https://www.youtube.com/watch?v=6wxHpUVcGFc|video] that may help with the disassembly.
As for parts the only parts online seem to be filters.
If after disassembling it and you can get to the fan motor OK, check the windings with an Ohmmeter to see if there's continuity through the windings. If the motor is faulty sometimes the fan's make and model number is found somewhere on the fan itself. Search online using that information to hopefully find suppliers.
If the fan motor tests OK you may have to see if power is getting to the fan when required, by chasing the wiring back to the control board.