This method requires:
1 - Enable "Developer Options" and USB debugging enabled.
2 - Computer running Windows, MAC OS or Linux
3 - USB cable
Note: Check the availability of your mobile service provider, in some cases it may be that VoLTE is not included in your locality.
Enabling Developer Options:
Settings -> System -> About Phone -> Software Info -> Build number. Tap on the section 7 times
Settings -> System -> Developer options -> USB debugging -> ON
Connect the device to the computer, open the command prompt or Terminal (Linux or MAC OS) and perform the commands below:
First verify communication with the cell phone via USB cable:
On your device screen will a "Allow USB debug?" Prompt appear, you must confirm the OK button.
Enable VoLTE in Build.prop
adb shell setprop persist.dbg.ims_volte_enable 1; setprop persist.dbg.volte_avail_ovr 1; setprop persist.dbg.vt_avail_ovr 1; setprop persist.dbg.wfc_avail_ovr 1
How to check:
Settings -> Connections -> Call -> Wi-Fi calling -> On
Settings -> Connections -> Mobile network -> Enhanced 4G LTE Mode -> On
Disable VoLTE in build.prop
To disable, just follow the same path to enable, but this time you should change the command by this below:
adb shell setprop persist.dbg.ims_volte_enable 0; setprop persist.dbg.volte_avail_ovr 0; setprop persist.dbg.vt_avail_ovr 0; setprop persist.dbg.wfc_avail_ovr 0
I believe it is necessary to add and modify files in the system. Unfortunately, I can not work on the rest of this project.
If anyone can contribute can share knowledge, maybe we can improve and make this feature functional.