@Puskistolero92 if your firebase users have google accounts linked to them, then theres a few ways to implement the Google sign in step, but this library doesn't manage that for you as far as I know. Theres a few guides on how to implement Google single sign on such as:

https://medium.com/@arezoo.nazerdeylami/implementing-google-sign-in-with-kotlin-and-compose-multiplatform-8fad1898b866
https://proandroiddev.com/integrating-google-sign-in-into-kotlin-multiplatform-8381c189a891
https://euryperez.dev/compose-multiplatform-login-with-google-cc3217a99349

And a library that can help is https://github.com/mirzemehdi/KMPAuth

After the google single sign on is complete, your app receives an id_token and access_token, and to log into the firebase user you can do the something like:

import dev.gitlive.firebase.auth.FirebaseAuth
import dev.gitlive.firebase.auth.GoogleAuthProvider
val tokenResult = googleAuth.signIn() // implementation you chose for google single sign in
val cred = GoogleAuthProvider.credential(tokenResult.idToken, tokenResult.accessToken)
val firebaseResult = auth.signInWithCredential(cred)