There is a plug on the water tap, usually pull up to direct the water flow to the shower head, push down to direct water coming out from the tap. Now, the plug malfunction, cannot push back to the original position. So, water coming out from both shower head & the tap. I cannot disassemble the plug, don't know the structure. How to fix it? Advise, better with diagram showing the structure of the tap. Thank you. Calven Ip Fm HK