Hi, Bekka. Condolences on your grandfather's recent passing.
The trick is that you have to add his DNA test information while viewing his profile using the main menu item labeled "Trowbridge-2266." Under that, you'll see a submenu item labeled "DNA." Clicking on that will take you a page titled "DNA Ancestors View for Walter Trowbridge." Third from the left under that title will be an option labeled "DNA Tests."
Click on that and, as profile manager, you should then see the DNA test entry page you're familiar with from adding your own information.
It's good to know the sequence of steps in case you ever need to do it again, but this shortcut should take you to the right place: https://www.wikitree.com/index.php?title=Special:DNATests&u=39165733.
Using the main menu item "Add" and then "DNA Test Information" won't work because it will always default back to your own profile, not the person's profile you're viewing.
Hope this helps!
