If you no longer have access to the device with which 2-factor authentification was activated, you can request to receive a recovery code with the recovery channel that you've set up.
To do so:
Log in as per usual.
On the 2-factor authentication page, click on Troubles with your two factor authentication? Recover.
A recovery code will be sent to your recovery channel (email or phone number). Enter it and you'll be logged in.