Please access the Calendar app, then go to: 


Options > Settings > Add Account and choose Google


Next, enter your email address and the password from your Google account and press Save


If you see an error message and have a problem logging in, please check your email inbox, as you may receive an email that the sign-in was blocked. In this case, please allow access to less secure apps in your account settings in order to sync your calendar to the Calendar app on your device. 


Please note that if you have a 2-factor authentication enabled for your account, it is not possible to toggle the less secure apps access in the Google account, so the calendar account on your device won't be added. You can choose to disable the 2-factor authentication and follow the steps above to fix the issue.


The account with a 2-factor authentication can be used successfully with the other Google services on the device.