how to turn backlight on for BC1202A LCD
Which version of backlight do you have?
There are 4 versions: LED edge yellow/green, LED array yellow/green, LED edge white/blue, EL / white(blue). It depedns on that. Edit: Look at page 3, numbering system to make sure.

The option b shorthand is: you have some jumpers on the module, you can short jumpers 1 and 2 and open jumper 15 to connect the backlight to the module's power supply via RL (which needs to be changed to an appropriate value). The jumpers most likely are solder joints.

Things change a lot if your backlight is version EL white or blue, because EL needs a high voltage generator (110Vac 400Hz).