For SSL Certificates purchased directly via whmcs.com You can reissue your certificate for a new server or installation at any time via the self-service Digicert portal here:
https://www.digicert.com/account/guest-access/?c=dxcdmsvfv13hc661q2dx90yd2wfkv299
For SSL certificates purchased via WHMCS MarketConnect, please refer to the MarketConnect Managing SSL Orders knowledgebase category for more information:
https://marketplace.whmcs.com/help/connect/kb/digicert_ssl_certificates/managing_orders