The IRS will send you a letter of explanation for the offset. Please see these TurboTax FAQ's for more information: https://ttlc.intuit.com/community/refunds/help/what-is-a-refund-offset/00/26301
https://ttlc.intuit.com/community/refunds/help/why-is-my-direct-deposited-refund-or-check-lower-than-the-amount-in-turbotax/00/25594