In the Third Age, all the best families had heirloom blades handed down from generation to generation, graven or inlayed with ancient runes. The runes usually said something like this:
In case of Nazgul, insert blade. If you are a living man, please find the nearest person that isn't, and ask them to insert blade. Possible options may include dwarves, elves, hobbits, ents, orcs, wizards and helpful undead with a debt to repay. Or, and this is a wild shot but hear me out, maybe you might find a female who might insert blade. While inserting blade, please wear safety glasses and protective clothing, as blade is likely to explode in shards of flaming metal. Other side effects of inserting blade may include numbness, disorientation, confusion, coma, and a temporary or permanent impairment of your will to live.
If possible, insert blade some place in the Nazgul likely to terminate the Nazgul, because, if you've been paying attention so far, you understand that your first attempt may be your only attempt.