It sounds like you need to complete the Missouri Certification of Rent Paid (MO-CRP) form before finishing your taxes. Here's a quick guide to help you out:
Obtain a copy of the MO-CRP form from your landlord or download it from the Missouri Department of Revenue's website here
Enter your Social Security Number, name, and rental address.
Provide your landlord's name, address, and phone number.
Specify the months you rented the property.
Enter the total rent you paid.
Choose the type of rental (apartment, house, etc.) and enter the percentage.
Multiply the gross rent by the percentage.
Multiply the net rent by 20% and enter this amount on your MO-PTC or MO-PTS form.
Make sure to attach the completed MO-CRP form to your tax return.