Are there any recommended products for bluing ? Not for scratches but general wearing. Do they work ?

I find this stuff works pretty well

https://caswellplating.com/black-oxide-kits.html

It isnt actually bluing, but it does make carbon steel black

I'm really looking for something to "touch up" if there is such a thing.

These videos from Old Path Traveller may be of help -

-using Birchwood Super Blue to reblue a part:
https://www.youtube.com/watch?v=u_9vUukXNww

- rust reblueing entire pistol, then uses Birchwood Casey Perma Blue to finish:
https://www.youtube.com/watch?v=EqR9aSn7U4o

Although the second video is really a summary instead of a step-by-step how-its-done, it was still very informative. Especially using the cold blue on top of the rust blue to add more luster.

I'll have a look, thanks.