how can I control the chord progression of a software loop using a midi keyboard

In the browser loop list under "rock/blues", the "70's rock ballad piano" comes in the chord of "C". I want to be able to control what chord it will be based on the different chord progressions of the melody. does anybody know how I can do this? In other words I want to be able to control the chords of the piano playing with my midi input.

Can anyone help?