In firebase I can create users in a registry
AngularFireAuth.createUserWithEmailAndPassword(email,password)
But when using this method, the current user changes and adds it to the session automatically, but what I want is to create many users at the same time without losing the one I already started, how can it be done?
What you need to use is the sdk admin of firebae: link
So that code is handled on your back-end with NodeJs, Java or Python. The documentation is very clear.
Hence, what you would do would be to expose a method in a REST service for example that you send from your Angular Front-End application to manage your users in a massive way.