Help with my 2012 compliant britax marathon

[countrymum]

Ok, my daughter made a mess of her seat today so dh took the fabric off for laundering, with it came in a piece of foam, my problem is I don't know where the foam goes? Is it for the seat or the back? I need this seat back together by 9am and I want to do it right but my manual don't show the foam and it was not attached to the seat. I wonder if it was added on the new seats? Can someone look at theirs and please lmk? It's square with a narrow slit in the middle cut out so it is in the shape of a lowercase n.

 

[lovemy2kidstw]

It goes on the bottom, where the child sets. The buckle goes through the opening of the 'n'. There should be a piece of elastic on the underside of the cover to put the foam.