google account without gmail

I have an imap email account @gmx.com, the same email adress is my google account.
How can I syncronize the calendar?

thanks

Hello Jens,
I am not sure what you’re suggesting, is this a google account or not? Does the automatic setup not recognize a calendar for the gmx.com account? Or do you wish to use the same calendar for both accounts?

Best regards,
Olivia