Short answer
Open the app and check the main screen. It shows the remaining data for your current plan.
What you may see
Remaining data.
Plan name or destination.
Validity period or expiration date.
If the numbers do not update
Close and reopen the app.
Make sure your phone has internet.
Check again after a minute.
Important
The plan includes the total amount of data for the full period. It does not reset to the same amount every day unless you have a daily subscription.