Please help! All my claims are getting denied. Which form do I have to fill out to upload my rendering NPI to my provider file? Also how do I upload it?

I just received several error codes with the message “Rendering NPI not on file.” I found a help page but when I click the listed link, it just gives me a list of forms with no real instructions. It doesn't specify which form to fill out nor where to submit. Please send help as this is urgent. Thank you so much!