Chosen Solution
I have an iPhone 7 Plus with no home button so I cant set it up. How can I set it up using a computer. When I plug in an iCloud Locked 6S Plus it shows up with the activation screen on the computer but when I plug the 7 Plus in it doesn’t show anything.
You could activate Voice Navigation (in iTunes). That should allow you to get into the home screen. From there, configure the Assistive Touch in Settings/General/Accessibility/Assistive Touch.