Question How can i Flash K750, and upgrade its firmware: No signal


I got my old k750, which doesnt show signal coverage. It says "No netw. coverage".

SO i repaced the antena fle with a new one today.

But still it shows that "no network coverage" or "searching" error.

As i have read online, now it should be a problem with the firmware.

Please help me to find a guide on flashing k750.

I already tried
XS++(doesnt detect my phone)
setool3 (it says, "card not found)
Davinci Flasher

^^ I dont know what files should i input to DavinciFlasher. I dowloaded few firmwares from TopSony but those filetypes mismatch with DavinciFlasher's input types.