To resend a Certificate on the website you will need to know the Job Address, however you can use the Customer details or the Job details, though these may prove to be a more difficult option.
Click on the Job Address tab.
Search for (or browse to) the Job Address for the Certificate you wish to resend, then click on it.
You should now be on the page for the Job Address. Select the "History" tab.
Find the certificate you wish to resend under the "History" tab, then click the Flame Icon to the right of it.
You will now be viewing the certificate. If you scroll to the bottom of this page, you will see several options. Choose "Resend".
On the next page, if you are happy with the email, choose "Send Email".