You won’t get a response, that account is retired says so on the profile when clicking the pic.
And these are peer-to-peer forums , shopify staff rarely shows up anymore here.
The new link is https://help.shopify.com/en/manual/online-store/themes/theme-support/theme-support-customization#add-how-did-you-hear-about-us
But it is no longer a tutorial, try internet archives to try and find it
If you still have design-time left , of your 60 minutes free desing time for basic and up plans.
https://help.shopify.com/en/manual/online-store/themes/theme-support#shopify-design-policy
Then shopify support may be able to do this for you.
There’s also an older post for vintage themes that may be applicable for the code savvy.
https://community.shopify.com/t/cart-add-an-agree-to-terms-and-conditions-checkbox/7540
Or you can reach out to me or other devs for services to set it up or sponsor creating a modern post tutorial.