Presumably the amount you want to claim is somewhere in between what you originally claimed and the proposed IRS adjustment.
In that case, prepare an amended return showing your correct figures, and send it to the office that sent the CP2000 notice, along with a letter explaining your changes and a check for the difference in tax. Explain in the letter that you paid for required books and supplies that increased your qualifying education expenses to more than the billed tuition, but that you did use the wrong figure and have sent an amended return with the correct figure for the credit which includes tuition plus books and required supplies. If the CP2000 asks for proof of your expenses, send receipts; otherwise I would not send the receipts but I would indicate that you have receipts if they want to see them.
Amending instructions are below,
Amend https://ttlc.intuit.com/replies/3288565
