Navigate: Settings > Network & Internet >Mobile network .
Tap Advanced then Preferred network type.
Tap the appropriate setting:
LTE/CDMA: This is the default setting for this device.
LTE/GSM/UMTS: If available, this setting should only be selected if experiencing service issues in locations that offer multiple network types and only LTE/GSM/UMTS is needed.
The preferred international carrier is automatically selected.
You can manually select an alternate carrier but it may require as many as 6 registration attempts with that carrier prior to successful registration.