For this exchange, since the trade fees can be in a third currency, please import the file twice via Custom Exchange Import with the following settings:
Only trades
Only fees
After import you need to bulk edit the transaction type for the fees to "Other Fee" by the exchange and the trade-group as described here: Bulk Edit/Delete - Instructions.
Save each setting by clicking on the "save" button after putting the file format and parameters exactly as shown in the screenshots so that you can just load the saved settings if you want to import more MEXC files in the future.