where to evaluate and sell large chess collection?

If you post some pictures here then people will give you an idea of the value.
I think eBay is a good place to sell chess stuff, but you will need to describe them properly in order to get your listings visible to the right buyers. Lots of knowledgeable collectors haunt these forums so we will be able to help with this.

I don't think you can do it from the App, if that's how you've connected. If you're connected via a browser you should be able to do this via the "Insert Image" Icon - see pic below...

Alternatively you could join the Facebook group "STAUNTON CHESS SETS VINTAGE & NEW Post your sets". Lots of knowledgeable people there.

Alternatively you could join the Facebook group "STAUNTON CHESS SETS VINTAGE & NEW Post your sets". Lots of knowledgeable people there.
Very valuable recommendation by @IpswichMatt, as the number of collectors active on Facebook is significantly larger than on the chess.com forums. I might only add that the "STAUNTON CHESS SETS VINTAGE & NEW" group on Facebook is mainly dedicated to Staunton type chess sets as the name already suggests. Should the collection consist of different types of sets, which I can only assume, I suggest to (also) join the "CLASSICAL CHESS SETS NEW & OLD" Facebook group (run by me, inter alia) or the "Chess Collectors" group.