From a Home screen, navigate: Apps > Settings > More.
Tap Mobile networks.
Tap System select.
Tap Network mode.
Tap the appropriate setting:
LTE/GSM/UMTS When LTE/GSM/UMTS is selected:
Tap LTE/GSM/UMTS settings.
Tap Network submode.
Select one of the following:
LTE/Legacy 3GPP multi
Tap Network operators. The preferred international carrier is automatically selected. You can manually tap an alternate carrier but it may require as many as six registration attempts with that carrier prior to successful registration.
Select either Search networks or Select automatically.