If you actually need no other Federal or state forms, this link goes to the form and you can fill it in right on screen, print and mail it for free
https://www.tax-brackets.org/missouritaxforms/form-mo-ptc
Otherwise, you can fill out the federal Personal Info to say you are a MO resident, download the MO tax program, and then go to Forms. Up above the forms list on the left, enter the name of this form and it will pop up on your screen and you can fill it out, print it and mail it in.