You can write your topic however you want, but you need to answer these questions:
What do you want to achieve? Keep it simple and clear!
I want to know if it’s possible to have PathfindingService use nodes I already created instead of creating nodes for itself, as well as how to do that.
What is the issue? Include screenshots / videos if possible!
Currently have no idea.
What solutions have you tried so far? Did you look for solutions on the Developer Hub?
I came up with my own solution but is likely more complex. This sounds like something that probably is already in the background, just maybe not well documented.