Using handsets sourced from BroadNet you should not need to use this feature however you sometimes change it my accident and need to change it back.
Press and hold on the top bar (or press # on non touch screen handsets) to open the options menu.
Press "HW ptt"
You will now be prompted to set the PTT button.
Press the button you want to act as the PTT button to proceed.
Please note: Any button you press at this point will become the PTT button, including the power and back buttons - please show caution before proceeding.