If someone does not receive his email confirmation, how would I go about adding a way to resend the confirmation email?
You can execute SendConfirmationEmail method of the AuthController
How would I go about filling this up in Radzen?
Or should I make a C# method for it? If so how do I do about setting it up exactly?
Any options here? How would I go about grabbing these parameters for the function?
You won't be able to execute this method directly from Radzen as it uses parameters that need to be injected. Check the implementation of the AuthController class and reuse the logic in the ServerMethodsController class.