Reset data usage.

Hello.
How can I reset data usage?

Thank you.

Try Following Steps
1.Open Settings
2. Select Data Management
3. Select the blue text under the words 'Data Usage Notification Settings'
4. Enter your required data allowance, early data limit notification and monthly reset date

Check this Link for further details
How to monitor and manage mobile data usage with BlackBerry 10.3 | CrackBerry.com