Thanks for sharing your question with our network, @prairiefiberart !
In addition to helpful comments shared by fellow user, @yashgarg , I’d like to add that perhaps the reason you are unable to see the “Add” button is that your screen might be minimized or hiding it. Simply scrolling further down or expanding the window might help you see the option. If the issue continues to persists regardless, then make sure to clear your cache and cookies and try again to make sure all the page elements are loading.
If you are using the mobile app to add the discount, then you can select “done” in the top right-hand corner after selecting the products. That should work, but please let us know if you have further questions.
Warm regards,