I'm not quite sure what you are asking for. Are you using FusionAuth hosted login pages? If so, the 'sign in/sign up with google' button should be present for any FusionAuth application you've configured it for.
If you are not, you are responsible for starting off the sign in/sign up process on your own and then calling the 'complete login' API as documented here: https://fusionauth.io/docs/v1/tech/apis/identity-providers/google#complete-the-google-login
Which approach are you taking?