How to access Samsung J1 (SM-J100H) service mode to change 3g bands

Hi!

I got this phone (SM-J100H) in Ecuador and now, back in Argentina, I found out that it is not able to connect to 3g networks. As far as I know, here in Argentina the 3g bands are 850-1900, while the specs of the phone state that it works for 900-2100 :/. I couldn't find any concrete information on how to change the bands (or if it's even possible for this specific phone), but it seems that there could be some option in the "service mode" menu. Anyway, I'm not being able to access it. Apparently, I should be able to do so by dialing *#0011# and then doing some kind of trick. For example, going "back" and then giving the keyinput "Q" and then "0000". Also found some other guy who said that you should go "back" and then giving keyinput "1". Neither worked for me despite the phone is rooted.

Details:

Android version: 4.4.4 (stock, came with the unlocked phone)
Baseband version: J100HXXU0AOF2
Kernel version: 3.10.17-333157 dpi@SWDD5808 #2
Build number: KTU84P.J100HXXU0AOF2

Does anybody know how to access this menu and/or if it may let me change the 3g bands? Or better, how to change the 3g bands, if it is even possible?

Thanks in advance!