If it was a Zippo, I'd spin the strike wheel backwards with the tension spring out. Should work
on a Nimrod I think. The flint should fall out. You may need to use a sewing needle to coax/guide
it out.
If it's one of those 'bolt' looking types, it's just a novelty lighter... not really serviceable
in my opinion. I can't stress enough how much better matches are unless you're outside in the wind,
then I go to a Zippo.