How do I receive my $15 Wells Fargo discount, if I'm already a TurboTax member?

To get any sponsored discount, you must always enter Turbotax though the special link at your provider's web site. You can not get the discount if you prepare your return using the Turbotax.com web site. See this Turbotax FAQ:
https://ttlc.intuit.com/replies/4652791

There is no other way to get the discount.

That did not work for me

WHAT IS THE SPECIAL WEBSITE PROVIDED BY THE BANK!!!! WELLS FARGO KNOWS NOTHING ABOUT THAT!