Your lender must give you an adverse action notice, which explains the following:
The adverse action notice will explain that you can request a copy of your credit report from the credit bureau that provided it. If you believe the information reported is incorrect, you should file a dispute with the credit bureaus. If you aren't sure how to proceed, contact the lender that denied your loan application.
Phone: 800-613-6743
TDD Number 713-658-0340
TTY: (800) 877-8339 (via a relay service)