Google just reverted me to the new calendar. When I click on the gear, I don't have the "classic" option anymore. I hate the new format. Anyone have any ideas.
It's not possible.
And according to this G Suite announcement:
In this phase, users will still have the option to opt out of the new UI until February 28th, 2018, when all users will be fully upgraded.
It doesn't seems to be possible.
Have a look at this thread where more people are angry about it.
According to this it says that there should be a button to go back to the classic one but since the button is no longer available, we can only assume that they don't want us to go back to the old one.
You cannot go back to the old Google Calendar. Even if it is possible (which it's probably not), you will have to use this version in the end. It's like with the new Gmail: you can go back to the older version of Gmail but once the new version is official released to the public, you will no longer be able to go back to the older version.