First check your backups and see if you can re-install the "private key". 
If you don't know how to re-install the key from your backups, then contact your systems administrator. 
Failing that, contact your web server software vendor for technical support. 
The only alternative course of action available is a re-issuance of the certificate following the re-submitting of a replacement CSR.

To re-submit a CSR please submit a ticket at https://customer.globessl.com/submitticket.php include the CSR, order number and reason for re-issue.