In your menu, go to the 'Change Zoid' option. Once there, you will see a list of all of the Zoids you currently have. Select one, and you will be taken to a list of all pilots currently in your party. Select the pilot you wish to place in the selected zoid. You will be taken to a screen that shows what affect that pilot will have on the zoid's stats. Blue numbers show an increase, black shows no change, and red shows a decrease. Pressing confirm once more will bring up a final check to be sure you want the pilot to be in that zoid. Confirm the choice, and the pilot will now be assigned to the zoid