The amount that you earn is not reported on your credit report. Only the credit accounts that you have and use such as your credit cards and the loan accounts are reported on your credit report as well as the payment history which constitutes your credit history.
A credit report does not contain any details about your income. If a lender denies your application for credit based on your debt to income ratio stating your income is too low then the information that he has about your income has to have come from other sources and most probably has been provided by you along with other documents. You will need to discuss the income details with the lender and how you are planning to consider it with the additional debt that you are planning to undertake. All lenders considered a certain death to income ratio before approving an application for credit.
If the lender disapproves your application for credit based solely on your income then there is nothing that the credit bureau can do to help you with that. However if the lender also considers other information present on the credit report based on which he denies you credit then the lender must inform you of the factors that has it was his decision and also give you the instructions were accessing your free credit report from the credit bureau that your credit report belongs to. Whenever an adverse action is taken against you such as denial of a credit application based on the information present on your credit report you automatically become entitled to a free personal copy of your credit report. It is the job and is the duty of the lender to inform you of this as well as provide you with instructions to access this copy.
When you access your personal copy of the credit report you also get instructions on how to dispute information that you think is in error.
If the reason for denial of credit was some information on your credit reports that you believe is inaccurate or outdated you can disputed with the credit bureau online or seek the help of a customer care representative on the phone.