You set the rocker arm to valve clearance buy using 0.04mm and 0.10mm feeler gauges. The thin one fits and the thick one doesn't. O.S. sells the tool kit with the small wrench, screwdriver, and feelers:

OSMG6334 72200060 GAUGES TOOLS 4-STROKE US$10.99

Set the clearances when the valve is off the cam.