I received this e-mail below a few days after I already filed with TurboTax. How do I claim my $15 discount since I claimed a Robinhood product and I already filed?

This is the e-mail I received...
"We’ve partnered with TurboTax to offer a $15 discount on TurboTax Premier federal products. When you visit TurboTax through Robinhood, you can get a $15 discount on tax filing services."