There will be 2 screws holding the circuit board down and some spade connectors. remove the 2 screws and the spade connectors (noting where they were connected). Next Located the neon bulb and it's resistor mine are in the picture below circled in green.
on the opposite side of the circuit board de-solder the bulb (red oval) and resistor (Green circles), if your bulb uses the same resistor leave the old one.
Install new bulb and resistor (if needed) and solder them in place, do not push the neon bulb all the way through the hole. Make sure the neon bulb wires are not touching each other and install the circuit board back in the plug strip.Carefully push the neon bulb through the hole as far as it will go. double check your wires are not touching, and re-attach the spade connectors to the switch and board. If the spade connectors are loose use a pair of pliers to lightly squash the female connector before installing them.
close everything up. I replaced the proprietary screws with regular screws of a similar size. Apply power. When switched on the bulb should glow and no longer flicker. If it still flickers or does not glow you messed up somewhere, your replacement bulb maybe bad, and I cannot help you.