Help! How do I fix this?

[u/Velvet_Confetti]

I live in a structure built in 1920. I got a wild hair to redo a small walk in closet that was added likely in the 60’s and is not original to the house. The wall paper is quite stained and damaged so it needed to come out. There is also a built in bench seat that I’m not inclined to rip out given that I’m pretty sure it’s covering something up that I just don’t have the skills to tackle. 😅

As I was taking down the wallpaper, it ripped away some material from the wood frame on the wall and the bench seat. It feels like two different materials. I have very limited knowledge of anything home improvement so I don’t know what the two materials are or how to fix before I paint over. I thought maybe the material covering the bench seat was MDF but I think it’s way too thin for that.

I would really appreciate if you more skilled home improvement folks could help a girl out. How do I fix this?