If you purchased the test yourself, you can reprint your certificate at any time by logging onto www.marlinstests.com and selecting "Results & certificates" under the "Results & certificates" heading at the top of the home page. On this page you will be able to search for any certificates which have been sat on this account, and can choose to (re)print as necessary.
If your company or manning agent purchased the test for you, please contact the company in question. They will have a copy of your certificate in their account and will be able to send it to you. Marlins is unable to send you a copy due to data protection.
If you took your test at a Marlins Approved Test Centre, you must contact the centre yourself, as they will need to stamp, sign and reissue a certificate for you.