You can shift the tray on a row buy using the arrow icons to rotate through the 9 rows. And you right-click and drag power icons to move them around the hot tray. And to remove an icon, right-click and drag the icon anywhere on off the hot tray and release.
On the bottom of your screen there should be a row of ability slots, 10 slots long. Look at the last slot, all the way on the right. There should be a tiny little square button at the end of that row, right next to that last ability slot. Click it.
It should bring up a window that lists all of your available abilities. You can drag them onto your ability slots in any order you like. Your Shield Distribution abilities will be in there too.