Why I can't change my preferred network on HTC one m8?

[abu omayer farnan]

When I enter this number*#*#4636#*#* it takes me to the phone information where I found the drop down list of preferred network types. My phone is showing no service and it was on wcdma/GSM/LTE (auto) . I was clicking on wcdma preferred but nothing happens. Can anyone help?

 

[methodman89]

Maybe because your carrier is locked to GSM. Can't choose what doesn't exist, even if it's on the menu.