Victorinox or Wenger SAK?
If former you can send it in ... I think ...
Rust can be removed with steel wool, a bit of light oil (Mineral oil or 3 In One) and a little elbow grease. It may not be mirror polished (hence not a fingerprint or smudge magnet, and might not be usable as a signal mirror anymore, but will be rust free.


After removing the rust, lube the joints and put a thin coat of oil on the blades and tools.
Most will tell you:"Use a food grade oil like mineral oil it there is even the slightest chance of using it for food prep or eating."
I don't bother For the last 62 years (since age 5), I just used what I had/have available: new or used motor oil, or transmission fluid, 3 In One, gun oil, WD-40, Olive Oil, Mineral Oil, used bacon grease from the grease pot on the stove ...
After wiping off the excess oil, there isn't enough left on the blade to matter.

I've never gotten sick from using one of my knives to prep the food, or cut it to bite size at the table, no matter what I used to wipe down the blade.
I doubt I've consumed as much as 1 cc of non-food grade oils over the years from using my knife on my food.