sharpening hardened steel especially conical brurs is a very precise
action to be performed.
A file is out of the question. might as well have cleetus and porksword
give your car a valve job with sand paper and lapping compound. same
goes for a sharpening stone / pen, whatever..
you will ruin them much worse then they are now if you even try. there
are precise angles, etc etc. you need a lathe, a programmable CNC
preferrably to even have a shot at doing it right. You are talking
measurements of a few thousandths of an inch, and I don't care who you
are, NOBODY can see that reliably just glancing.