https://help.zerossl.com/hc/en-us/articles/360060119933-Certificate-Revocation
edit: oh you prob out of luck
You can revoke any certificate issued via the ZeroSSL portal. Currently, certificates issued via ACME can not be revoked from inside the portal - please follow the instructions of your ACME client for revoking those certificates.
the gui in pfsense does not have the ability to revoke - you prob have to move the certs to something you have certbot installed to and revoke that way.