I had to Google Mickle mixer, I thought it was a Mackie.
Anyway, you should consult your Mickle mixer's manual. Identify the inputs, the outputs, and familiarize yourself with the controls. Do this with your Platinum and amp as well.
Start small, connect your Platinum to your mixer and connect your mixer to your amp (with speakers connected) and turn down all volumes before powering up. Baby steps at first and once the whole setup is playing then you can fine tune everything else.
Good luck