How to remove App Service Certificate resource
Go to azure resource portal (https://resources.azure.com ) and navigate to subscriptions --> specific subscription
--> providers --> Microsoft.Web --> certificates and see if it is here and i think you can delete it from here directly.
Delete a certificate in Azure Resource Explorer
- Access to: resources.azure.com
- Expand "Subscriptions"
- Expand "Resource groups"
- Look and expand the resource group where the certificate is
- Expand "Microsoft.web"
- Click on "Certificates"
- Choose the certificate you want to delete
- Make sure you have selected on the top read/write and then hit on "Delete"