How to create a standard LetsEncrypt certificate to use with subdomains of Multisite?

Hi all, i have generated a certificate to use with the main domain of my network, has i use multisite with subdomains the other hosts will not use the same certificate, is there any way to add more hosts to the certificate?

Also, if i want to install a new certificate to use with other subdomain which is mapped for a domain name how can i generate a new certificate with letsencrypt to use with for that domain name?

Thank you