Hello,
Thank you for contacting the support, and sorry for any inconvenience that might have been caused due to that.
Once you sign up using the Gmail option, you will receive an introduction email containing a username and password combination that you can use on your site.
Please check your spam folder for this email or alternatively you can reset your password using the password reset option shown below:

I hope this info helps.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.