user_id

Are you asking how to only update an author slug based on user_id, or are you wanting the author slug to be set to user_id?

2nd question
i want author slug to be set to user_id.

I would start here:

https://stackoverflow.com/questions/5040843/wordpress-author-permalinks

I’ve just added the ability to set an author slug to user_id on an experimental basis. It should work, but because I can’t test every scenario, I’ve labeled in experimental for now.