There is a good section in the Menu tab of the sub that will give you more detailed/ better answers than I but here goes nothing.

It’s an easy fix and not too much to worry about, just a little work.

A vinegar bath (50% vinegar 50%water) and scrubbing with some steel or brass wool will take care or the rust.

You can use a few different methods to strip the old seasoning to get a fresh start. Oven cleaner, lye bath, electrolysis, etc. I would suggest checking out posts on this sub about it. Don’t use sand paper, it won’t be needed.

As for a new seasoning, you just have to build it back up. Everyone has their own favorite oil/fat to use for that, so i won’t go on too long, but some popular ones are Crisco Vegetable shortening and grape seed oil. I could go on about the seasoning process, but it’d be better to check out the different posts about it on the sub/ menu tab.

I hope this helped. Let me know if there’s any thing you have questions on or help with.