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

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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?