Upon filing your tax return (not available afterwards), you will have the opportunity to apply for a refund advance; the FAQ's below provide further details on the application process:
https://ttlc.intuit.com/community/refunds/help/about-the-refund-advance-application-process/00/25557
https://ttlc.intuit.com/community/refunds/help/about-refund-advance/00/27333
However if you have already applied, and have been approved, you will receive an email providing you with details on how to access your temporary card for online purchases; please check your junk/spam folders also.