Use APKPure App
Get LTE to VoLTE Converter Pro old version APK for Android
Now You can convert your device to VoLTE.
This app is used to convert or add support of VoLTE to the LTE Device and also for 3G Phone to convert to 4G Phone Mode, This app is also used to help Jio Users.
also you can follow some other methods to convert the VOLTE.