You have to download the main generic k 770 i in download section firmware same version
R8BC004 cid 52 !!!
then generate the patch with this main using the patch generator of the forum....save the vkp file and put it on misc files ......then flash your phone with bypass security selected....
be carefull baterry fully charge and make backup of the gdfs original before.!!!!! saving in your pc ....if you whant to recover it if som. go wrong.
i sugest you to read and follow the instruction of unlocking in this forum..