My battery is draining fast since one month. I looked for the help and the iqoo customer care suggested me to to the battery calibration. This required battery charge 100 percent and then draining it fully till it switches off. After that charger is to plugged on till it is charged till 100 percent again. 

Problem:- when i plug my charger in the phone while it is switched off, it turns on automatically. View this, I am not able to do the calibration of battery. Please tell me how to turn this setting?