Recirculating door

Hi, these truck’s did not come with cabin filter so I went to the dealer to buy the door and cabin filter to put it in. When I finished putting the door and finishing up, I saw a white tube (below all the wires) that goes on top of the filter and it was open (see picture) but as I was closing it, I heard a plastic part breaking.
It is still in an up position and when I drive down the freeway, I hear air coming in to the cabin. The mechanic told me that I broke the air re-circulation door and it would cost me about $800.00 to fix it.

I wanted to know if it is the actual re-circulation door that is broken or something else? Because that white tube does not look like a re-circulation door. I need to know how to fix it?

Thank you