Is the Kobo a dedicated ereader or a tablet?
For a dedicated ereader, it should show up in left hand panel of ADE under devices when plugged in to USB and turned on.
If so, use menu/Help/Authorize Device to authorize it.
If not, check in your file manager whether it shows up as a mounted drive there, and post back here.
For a tablet, run an ereader app and that will have authorization withing the app, probably in Settings somewhere.
I have tried to authorize the kobo but the authorize function is not available even though it is a new computer running Windows 10
I am having the same problem - my Kobo appears in the left hand section, I can transfer and it says Unread but when I click on the Kobo to open the book it says it is not authorized. When I go into the Authorization section it confirms my computer is authorized and doesn't give any option for authorizing the ebook.