From within the Settings app, tap Network and Internet.
Tap SIMs.
Choose the SIM you'd like to change roaming settings for.
Scroll to Roaming.
Tap or slide the Roaming switch to ON.
Turning Data roaming on allows you to connect to data services while roaming. Turn Data roaming off to keep from incurring significant charges.
Tap OK.
Tap Preferred network type.
Select your preferred setting.
Depending on the age of your device, your available options may vary.
You've completed the steps!
