The felt strips are distinct from the seat pads. The strips feed into channels in the seat cover underside, to provide the classic rib contour. I haven't replaced some on my son's 190, but it seems straightforward. If they slid out, you should be able to slide them back in. Coat hanger, maybe?

__________________
Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K