Question on LP gas space heater down draft problem part 2

CRCgoodguy

Thank you for your help with my Warm Morning former question about down drafting.
I have another question that may have caused my problem. During the summer I cleaned the inside of my gas heater after disconnecting the gas and vent. Upon laying the heater on its side a piece of sheet metal fell out of the rear. I didn't think much of it at the time but now since I am having a down draft from the chimney and causing the vent safety switch to trip, I am wondering if this piece of metal was placed inside for a purpose. The metal sheet was placed inside the internal draft hood opening (see diagram attached part #9). Could anyone tell me how to replace this sheet of metal? The metal sheet was about 5"x 7". Thank you for all your help. Chuck