SMALL HELP please [ How to add WCDMA ONLY on huawei p8 dual ROOTED ] ??

Hello , i have Huawei P8 Gr-ul00 rooted and unlocked bootloader
I have only 4G/3G/2G MODE
Or
3G/2G(auto) mode
I want add
3G ONLY mode or WCDMA only mode
What i must change on system ? build.pro ? or band file ? Please help me what i must add to obtain this
I'm under 3G until it turn automaticly to EDGE , this make me crazy and i want destroy this phone :/

PLEASE HELP ME XDA members, you are my last chance