How does the U.S. government know where to send the money? If you have already filed a 2019 tax return (that’s the one most people are working on now), the Internal Revenue Service will use the direct deposit information on your 2019 return to send your payment to your bank account.

If you haven't gotten a refund DD'ed, there is a website where you can verify your ID and submit banking info.

https://www.irs.gov/coronavirus/economic-impact-payments