The Sectigo free e-mail certificate can only be collected from the machine and browser it was requested on.
If you have to re-install the Operating System (OS) and do not have a backup to the private key, then the current certificate needs to be revoked.
To have one of these revoked, please Submit a ticket. Please use the e-mail address that you have the certificate on as the registering e-mail address.
How do I back up my Digital ID certificate? (Windows)