s3 GT-I9300 install original firmware using sd card (recovery mode)

hello! i bought my phone (samsung s3 GT-I9300) one year ago in thailand. the wifi stopped working since i left the country (a few months ago). it says "saved secured" when trying to connect. i tried to restore the factory settings but it didn't help. i went to a small shop (no official samsung center in the town where i live, in the philippines...) and they told me that it's not the official firmware installed on the phone. they say it's not possible to install the original one as my usb connector has a problem and they can’t fix it.

my question is: can i install an original firmware for this phone using the sd card / recovery mode?

if yes, how?

thanks a lot! i spent already a few hours trying to figure it out...