How to remove rust from inside car

The other day I noticed how rusted the medal piece is that holds the passenger seat. It's only the front that is rusted. Any tips on how to remove it so it won't spread and get any worse? Can I use rust remover or sandpaper to sand it off?

The other medals in the car look fine because I looked.

Exactly as you've said wet n dry it off then use rust killer and then repaint with red oxide then top coat

Is this rusting a result of the dampness/water getting inside you mentioned in your other post?