when trying to authorize my computer and kobo reader message comes up saying "you can only authorize this computer w/an adobe id that hasn't been used on any other computer or mobile device. please try again

i'm unable to activate my kobo reader with ade.  my computer has been revamped and i had to reload adobe and when doing so at the question do you want to allow this on anything other than your computer and i replied no to this question.  how do i correct my mistake so that i can down load books to my kobo?