Sign into "contributor.stock.adobe.com"
On the black bar at the top of the page, click on "Contributor Account"
Scroll down to the bottom of the page, you'll see "Tax Information"
Download should take you to the forms
Otherwise follow the link at Account and submission guidelines at Adobe Stock under the heading "Account Creation And Registration", under the subheading, "Taxes", click on "payment and taxes".
On the new page select the appropriate heading.