Add a domain like this for the primary domain:
*.domain.com
The add the wildcard domain to that domain.
According to the following link, once you update the wildcard SSL for the domain/subscription “*.domain.com ” it will affect all subdomains.
https://support.plesk.com/hc/en-us/articles/213921605-Is-it-possible-to-create-and-use-wildcard-SSL-certificates-in-Plesk-