The control folder is in your main drive "Users" file. In that file look for your computer "name" , open that and then open "AppData" and then "Roaming", then "Microsoft", then "FSX" and you will see the "Controls" folder. You can copy the entire "Controls" folder and paste it into your Prepar3d folder (located in same Roaming folder under Lockheed Martin and let it overwrite those files but you might want to save those originals first.
You should then have all the control settings you had in FSX now in Prepar3d.