MG ZR 2003 Manual Heater only blowing Cold Air

One of my Friend brought Rover Street Wise 2004 it is fix with manual Heater Dials, either Dial set on Cold or Hot air it's only blowing Cold Air, but when touched on pipes across Heater Matrix Valve, pipe going under the dash is staying cold and the pipe coming from the Engine is extremely hot.

1st I suspect it may be Heater Matrix Valve who may have been out of order I took the valve off and operated manually but there was nothing wrong with it, the door was opening and closing when pressing on liver

then I put the pipes back on Heater Matrix Valve with valve door open so the hot water can flow through to Heater Matrix and Heater start blowing hot air but there was still no sign of hot air and even now the pipe was going under the dash was still cold and pipe coming from the engine was still hot

Just to eliminate the doubt I may have left Heater Matrix Valve door close, slightly loosen the clip on pipe going under dash, the hot water start leaking through other side of the Valve so the Heater Matrix Valve door was open

Look like it has air trapped in the system which is stopping Hot water flowing through.

Can any one please tell me the step by step procedure to bleed the Heater Matrix or any other way to bring Hot air back in car before my friend freeze to death

Thanks for reading