I purchased an app service certificate and would like to manage hostname in Subject Alternative Name(SAN) but unsure how it can be edited. Goal is to secure sub-domain using same cert without purchasing new one.
Currently managing\editing SAN for App Service Cert is not a supported feature yet. However, our product group is working on this requirement.
In meantime, as a workaround for your current issue our new free App Service Managed Certificate feature will help you to secure your sub-domain with a new certificate at no cost.
More details about this feature can be read here.
Note: This feature has it’s own limitations, However it should help unblock your current issue.