How I can link Playfab with an already existing Azure active directory B2C implementation of player accounts that I have created

Question

I have successfully gotten Playfab to work with my Unity app - I can create accounts and log in nicely. I am wondering how I can link Playfab with an already existing Azure active directory B2C implementation of player accounts that I have created? The existing Azure DB is used for players who sign up through a browser. Thank you for any and all help!