This will show you how to change PIN code settings for SIM Card in MIUI 7.
Instructions for other MIUI versions
In System Settings tap Additional Settings
In Security section tap on SIM Card name which PIN settings you want to change.
If you haven't changed your SIM Card name it will simply be name of your mobile provider. In this case it is: verizon
Now using Lock SIM card you can choose if phone should ask for PIN to unlock the SIM Card after each reset and Change SIM PIN option to change or set new PIN code.