Click on "Settings" and then you will find the following function on the right side:

Add your domain here and then create the CName.

If you have problems here and can't get any further, please contact our support and send us a screenshot with all DNS server settings.

If you are not sure how to find them, just google "CNAME provider". (Here you have to insert your domain provider of course).

In the backend of your domain provider, you must then logically also connect the CNAME.

There are detailed instructions from each provider.