I have host midi lead to Tyros 4 from PC windows 7.

I am attempting to get my Tyros 4 yamaha to start BIAB play back when I place my left hand to keyboard and not using the green play button, I have investigated the Tyros midi function button at External Clock and fiddled with the buttons but no luck.
Can someone please help and oldie (80years)with an idiot type sheet instruction on how to proceed.
(I play on top of the Biab program for enjoyment only)