The valve clearance specification for a 2000 Civic DX with a D16Y7 engine is as follows:

Intake Valve Clearance: 0.20 - 0.24 mm (0.008 - 0.009 in)
Exhaust Valve Clearance: 0.25 - 0.29 mm (0.010 - 0.011 in)

To adjust the valve clearance, you will need to remove the valve cover and use a feeler gauge to measure the gap between the valve stem and the rocker arm. If the clearance is outside of the specification range, you will need to adjust it by loosening the lock nut on the rocker arm and turning the adjustment screw until the correct clearance is achieved. Once the adjustment is complete, be sure to tighten the lock nut to the specified torque. It is important to note that proper valve clearance is essential for the engine to operate correctly and can affect performance and fuel efficiency.