Steve, that video relates to the GTS 300 which has a double throttle return cable.
Between 2007 and 2009 the GTS 250 was modified from a single throttle cable to a double one like on the 300.
Check if your model has the single or double cable, if it has the single cable, you need to take the headset off and you'll see there is a rubber cover on the cable that you can pull back to loosen the lock-nut and adjust the play.
Mitch Bergsma did a good video showing adjusting the GTV throttle cable, which has the same arrangement as the earlier 250's. The video can be found in the MV wiki section...
GTS Throttle Cable Adjustment
Andrew