Hi Alexander, thanks for posting
You can remove the small brass string guide with a flathead screwdriver, it’s just a wood screw.
I’ve already rough sanded the fingerboard and flattened it before sale. Just a quick hand-sand with a folded piece of 220 followed by 320 grit will have it ready for varnish. You could wrap a small flat block of wood with the sandpaper if you want to insure the fingerboard stays totally flat, but it’s not required in my opinion. Please post pics when you are all assembled!