IDE wrongly identify my Uno board as Mega 2560

You want the "board" selection to match your actual board. It shouldn't matter if the com port has the wrong "guess" about what kind of board you have - that's just info based on the USB VID/PID. It is easy for me to imagine a board that has been configured with the wrong USB info (especially if it's a clone of some variety.) But it shouldn't affect uploadability.
I'm not sure whether the IDE propagates the "guess" from the "port" setting to the Board setting; make sure it shows correctly in the lower right corner as per Bob's video. Perhaps re-set the board type AFTER selecting the port.