How to add a VM template that already exists

Hello everyone,

     I had 3 VM templates in my template library. But two of them disappeared from the template listing, but are still in the VM templates datastore. It would not be the case to import it, as they are already in the datastore defined for the templates. It would be a situation to add an existing template in the template library. How can I do this?

VSphere version: 6.7