This is done via the placement configuration menu. You can get to it via M -> Schematic Placements -> Configure. You can also access it by default using the hotkey Numpad Minus, which opens the GUI for the currently selected placement, if any. To change which placement is selected, click on one in the Schematic Placements list/menu, so that it has the white outline indicating that it's selected. You can also use the "tool item" and (while being in the Schematic Placement tool mode) middle click while looking at the placement in-world. You can also click with the tool to move the placement origin, or use Alt + mouse scroll to nudge the placement in the direction you are looking.