2002 impala pass lock/battery light flashing/weird black switch under below steering wheel underdash

2002 impala classic no start no crank with pass code lock and security light flashing. I have read about the bypass for the ignition. I looked under my dash below and found black on/off switch on plastic panel you pull out to get at wiring.could previous owners or owner have already done this modification. If anyone thinks this may be what the switch is for.. not sure of procedure is to get car started.
Would the switch need to be in on or off position etc. Do I have to disconnect baterry yo reset bcm or could the ignitionignitionswitch possibly have failed.
-car died week ago started with a boost
-baterry low recharged to full on trickle charger tried to start pass lock and security light flashing
-all instrument panel lights and ac/heater radio working

Read more about the PassLock bypass sequence, whereby the ignition is left on for ten minutes without cranking the engine - Three times.

Thanks for the reply.. I will give that a try. I have become familiar with the procedure from all the great advice on here. Have tried now to charge the battery twice now. It does not hold a charge. Battery dies fast. Curious though, when the battery fails does this cause the security passlock to come on? When change the battery will I have to do the bypass sequence?