How to update modem/BL to OK3 Currently i m on OH1(gsm unlocked) - Please help guys

Hi friend !

i want to get solution of my issue
i purchased l720t
while modem is OH1
and i live in pakistan !

i want to use Marshmallow roms for that i think i need to update boot loader & modem to latest version because on OH1 gsm is not working right now !

i just want to update modem / boot loader to latest version which is OK3 & also want to use GSM here in pakistan.
can you pleaseeeeeeeeeeeeeeeeee help me out to do this

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