How to become e a gods knight?

if you are already a saint do you go through trials.to become a gods knight or do you have to be born a higher status then any other cestrial dragons.

what about a citizen it seems anyone who is deemed worthy can be a cd like york who has knoledge to produce the mother flame. Even if she only eats and sleeps.she still has the brain of dr vegapunk couldn't she also try to become a gods knight if wanted?