There should be a spring loaded gas tap and an electronic pilot light ignitor button close to the little window where you see the pilot light . Turn off the boiler and turn down the boilers thermostat. Hold down the springloaded gas tap and push the ignitor button several times until you see the pilot light lit. Hold down the gas button for approx 20 second (or longer if unsure) whilst the pilot warms the thermocouple. When you release the gas, if the pilot stays lit , return the thermostat to its original position and put the power back on.If the pilot goes out , you need a new thermocouple. Depending on the age and the model , you may need to have the power on to light the pilot.