If the switch is bad you should replace it because you cant fix it. The hot wire leading from the 3 way switch circuit will have no power since all power must travel through the switches.
Multiway Switching Wikipedia
3 way switch not turning off light. 2 remove all wires from both switches. Each switch powers one or the other leg at all times. If one of the two 3 way switches toggles the light s on and off the other 3 way switch has probably failed. Light on 3 way switch wont turn off change switches already 1 turn power off for safety if needed. A wire getting loose in a terminal screw or in a wire connector at the switch or light fixture could cause the flicker. Be sure the wires are not touching anything and the bare copper ends are sticking out of the boxes and not touching anything.
Start by turning off the power to the switch circuit at the circuit breaker. Turn off the power and mark it so you dont confuse it with the 3 way circuit wires. Follow these steps to find which switch is bad. This can be caused by different events. 5 go to. If the 3 way worked right before then this will tell you what color they used as commonif its black as common tie your black to the red with a wire nut and go to the other end and touch the black to the red if the light doesnt work then touch the black to the other traveler wirewhite i presume this should turn your light on or off depending on the connection of black to either red or white.
This happens when there is excess energy leaking into the bulbs even when the switch is in the off position. 4 connect remaining 2 wires and connect to that same switch. In the latter one of the switches has likely gone bad. Disconnect all the wires from both switches. If the switch is miswired its easy to rewire. There are a pair of wires that run between the two switches.
Toggle each switch until the light come on. One of the wires in the two three way switches is always hot assuming the circuit breaker is on. Usually when a 3 way switch fails lights can be toggled on and off at one switch but not the other. Three way switches work by alternating the power connection between 2 legs called travelers. A corroded contactor inside the switch could cause the flicker but would also probably cause the switch to feel warm at the touch. If you turn off your lights and the bulbs are still glowing a little bit or one of the bulbs in your circuit doesnt want to shut all the way off you have what we call a ghost current in your circuit.
If a light switch wont turn off it could be because its miswired or just a bad switch. If one of the black hot wires does have power then that is the wire for the always on plug. You can test the switch with a voltage tester to determine which is the problem. 3 determine which of those 6 wires is hot and connect to dark screw of that switch.