By far the easiest way is to investigate which light isn't working & fix that! That's what the warning light is for. However, if you have replaced some of your standard bulbs with LED versions, there are various fixes. Essentially the warning is triggered when the car senses that a light circuit isn't drawing enough current. LED lights use significantly less current than standard bulbs so can trigger the warning. Look for CANBUS compatible bulbs or add ballast resistors to make the monitoring system see the correct current draw. On some models it is also possible to recode the computer system so that it does not monitor some lights so doesn't turn on the warning.