Implementing Login/Register in existing Blazor Server side Application

I need help with implementing Authorization, Logins and so on in my existing Blazor Application. This feature can be added when creating a Project but since I didn't know if I would need a Login/Registration I didn't implement it from the start.

Now I already have a Database, Api, and some pages that make requests to the Api...

I have tried these Steps but after creating the identity I could not migrate the new information to my Database. https://www.youtube.com/watch?v=FZzwhivKrtU&list=PL6n9fhu94yhVowClAs8-6nYnfsOTma14P&index=51

Is there any other ways I could try to implement this?

Kind regards, Aleks!