If you don't have the 6 digit code of the Google Authenticator (or similar) you'll need the recovery code that we sent to your email when you activated the "Two step authentication"
After this, go to https://panel.preyproject.com/session/new?lang=en , access with your email, and click on "Lost your mobile device?", there, you will have to enter the recovery code. Then, the two step authentication will be disabled and you'll be able to access only with your credentials
Let me know if you need further assistance,
Have a nice day!