Go to the the design view of your form; right click on field "Final Payment" and select properties, on property AfterUpdate, select [Event Procedure], then in the right margins click the little button with three dots in it and an empty subroutine will be built, to which you add
Forms!YourSecondFormName![Income Amount]= me![Final Payment]
Then close that window.
This assume the "YourSecondFormName" is open (it may be hidden) and that you've somehow positioned it to the correct record.
I suspect you haven't asked your question correctly. Is your question, "How do I get a data value from a form into another table?"