So my app has the option to sign in with Google. Upon clicking the button that Google provides, a web view opens and has the user input their credentials. After allowing the app
Yes, like @Rahul said following code would be the right way of going about it.
GIDSignIn.sharedInstance().signOut()
https://developers.google.com/identity/sign-in/ios/sign-in?ver=swift#sign_out_the_user