To add base domain click Add new domain:
On the opened page fill required field Domain name and optional fields: SSL certificate, SSL key:
In actual wildcard mode base domain has only one A/CNAME DNS record. This will be created when the base domain is being added.
Please note that certificate requires a *.<domain name> domain in common name or in alternative names header. In other words the certificate must be valid for *.<domain name>. The Key has to correspond the certificate. Otherwise domain will not be added.
Also, please note that SSL certificate and SSL key fields are optional. At the same time if you fill SSL field (certificate or key) the other one becomes required.
To delete domain, click on Recycle bin icon and confirm or decline this action in pop-up.