If it is patina I would just leave it alone unless it wants to rust.

If you want to reblue you will have to remove all barriers to the steel so that the new bluing looks good. I like to just barely feather my sanding/ steelwooling into the good bluing and make sure that is free of all oils dry and just a little warm not hot at all. so with all surfaces prepaired clean with hot water dry and then blue following directions.

I found the barrel being dry and warm helps. I use alchohol right before the final rinse.