How to make a "save" button a conditional also related to the user profile ?

Hello,

I have a page in my project where users can enter their information, with a "Save" button at the bottom.

What I want to achieve seems simple, but I haven't been able to get it to work for a week…

When the user (logged in via authentication) clicks the "Save" button, the action should:

• Create a new document in the "employee" collection (which I created in Firebase) if it is the first time the user fills in their information
  or

• Update the existing document in the "employee" collection if the user modifies their information.

Of course, these actions must be unique to each authenticated user. I'm not sure if I have set this up correctly in parameters, and I don't fully understand the logic behind it.

Could you help me and explain how these actions should work?

Thank you very much!