If you receive SSI by direct deposit to your bank account, the IRS will use that same bank account to direct deposit your stimulus payment. You do not have to do anything.

I couldn't add my direct deposit when I amended my tax return containing W2. How do I add my direct deposit information? I need the tax money as well as stimulus as soon as possible, cannot wait for mail checks. Thank you for your time.

According to IRS.gov:

In the coming weeks, Treasury plans to develop a web-based portal for individuals to provide their banking information to the IRS online, so that individuals can receive payments immediately as opposed to checks in the mail.

Please keep checking the above link for details. 

@gabeschwartz7

I already  did the  non filer  registration  with TurboTax,  what do I do now? IRS already  accepted the  filing. 

If you did the non-filer registration, you don't have to do anything else except wait for your stimulus payment.