How to modify CSC file of samsung sm-j500fn?

My phone origin is the UK and I am in Sri Lanka now. My phone modemst1, modemst2 were reset and also I forgot to backup.

dd if=/dev/zero of=/dev/block/bootdevice/by-name/modemst1

dd if=/dev/zero of=/dev/block/bootdevice/by-name/modemst2

After reset it has asked to unlock the network. I've tried many solutions such as flashing stock ROM of UK before I had custom rom(arrow os), zx3 tool pro. I could not do it. I don't plan to buy a code since I think, It can be recovered. I think it can be done via modifying the CSC file since it is specific to geographical region and carriers and it contains the software packages specific to that region, carrier branding and APN setting but I don't have enough knowledge to modify the CSC file. Another possible solution may be flashing the living country CSC file but I could not find CSC file only for my j5nlte phone with Sri Lanka. Can anyone suggest how to modify the CSC file or **provide any solutions to unlock the network in my device**? Thanks in advance.........