LG G8 (LM-G820QM) Unlocked

I have LG G8 Alexa variant. Model LM-G820QM. I think ts on latest firmware "qm21e". Right now I live in India so the VoLTE is not working. I tried to cross-flash it to Open firmware but LGUP gave error "Cant change the device(AMZ_US > OPEN_US)". I have three questions. Can...