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So you need both the frame of the damper and the flap. The flap is W10197773 as you indicated but the frame is part number DE72-40022A.
As for how to re-direct the vent, you will need to un-install the entire microwave and remove all the screws going into the outer shell of the microwave. The outer shell will then pull off and you'll see the blower fan motor which you can rotate to the back or straight up or straight forward (forward is for recirculating mode). This is how you direct the direction that the air will blow depending on how you want to set up your external vent.
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