From the Settings app, tap Network & internet.
Tap Data usage.
From this screen, you can limit your data usage and set up alerts for when you're reaching your data usage limits for the current month.
Tap or slide the Limit mobile data usage switch to ON.
Tap OK.
Swipe the data limit line to your desired limit
Tap or slide the Alert me about data usage switch to ON.
Tap OK.
Swipe the data warning line to your desired limit
Tap the Billing cycle dropdown.
Tap Change cycle.
Select your preferred data usage cycle reset date.
We recommend you match this date to the date your billing cycle starts to more accurately manage your data.
Tap Set.
You've completed the steps!
