DO IT WITH YOUR OWN RISK ,  I'm not responsible for your  bricked devices

Follow step carefully

New Method It maybe working for others device too

Requirements : build prop editor , or any root explorer with text editor on it

- find this one of below line on build prop
(+) ro.product.mod_devices=kenzo_global
(+) ro.miui.region=XX (xx could be any region)
(+) ro.product.device=kenzo (on MIUI 8)

- if you see one of the above  lines , put # on above line EX :  #ro.product.device=kenzo

-reboot your phone

NOTE: Kenzo = Redmi note 3 snapdragon, different device different codename
the line on build prop will  be different one and another rom

1. backup your rom with TWRP if anything goes wrong you can restore it back
2. Download Attachment TeleService.apk , Here
3. install root explorer
4. copy the file you've already download to system>priv-app>Teleservice
5. confirm overwrite , change permission to 0644 (rw-r-r)
6. reboot your device , if you got stuck at mi logo , boot to twrp , select reboot system.
Preferred LTE .zip

in some locale Volte options is missing in " sim cards & mobile network " example i'm using locale hongkong

Requirement :
1. Rooted Device
2. SQLite Editor

1. open SQLite Editor, files tab  , navigate to data > data > com.android providers.settings > databases

2. open Settings.db , Global  , search for Volte_feature_disabled
    change value from 1 to 0

3. close sqlite editor , turn airplane mode On/off , open settings > Sim cards & mobile network
    DONE

Source: MIUI