8.6 ohm resistor is decreasing 3.97volts to 2.95 volts which is connected to zener diode i can't understand how it is happening
Your simulated volt-meter is drawing a current, the magnitude of which suggests it has a simulated input resistance of 1Megohm.

The zener diode is drawing very little current, only 5uA at 3.97v. That's not consistent with a simulated zener set to 3.6v. Check what you've set its knee voltage to.

You could investigate the zener model by changing your voltage source, and see what current flows. Or get a better simulator. LTspice is the de facto hobbyists simulator.