

As most sites with a login you find your account settings by clicking your own name at the top.
Anyhow: you have subscriptions@geni.com as an email to contact, but you have to cancel your Pro in your account settings. In the welcome mail you also got instructions.
If you are in the Free Trial, see https://help.geni.com/hc/en-us/articles/229706247-How-do-I-cancel-m...