Hello there! I'm pretty inexperienced in this field and I think I need your support. My desk chair is made out of a single piece of 12mm thick plywood, bent and shaped to form both the seat and the backrest and then varnished to make the wood (which seems to be beech) look of a lighter colour.

This varnish layer has become sticky on the whole surface and has assumed a greyish/blackish colour on the seat, so the chair looks now quite disgusting although it's still perfect in all its other parts.

The best idea I came up to is sanding down by hand (and fine grit sandpaper) the chair and then revarnishing but I'm not sure if there are smarter ways to restore my chair.

What do you guys think about?