Hi there and welcome
This is for your Kindle correct?
Thats correct, as it is all linked to your Amazon account, not the actual Kindle itself.
You cannot transfer books between accounts, but what is stopping you from signing into your original correct account?
Ok, you need to actually register the Kindle with the old account again.
Which model Kindle do you have?
Once done, when you go to the list of the books, you select Cloud and you will then see them
Let me know the results please.
Can you please use my link below and reset your password
Once done, use this new password ***** the Kindle