You can make changes in the flight tickets as per your convenience, with How to change flight in ANA airlines. whether you want to change online or offline, ANA will tell you every step- ANA change flight online - Pessengers have the liberty to make the change online while sitting at their homes. Visit the official website of the airline then give your details then check your bookings then pay the amount.

https://airlinespolicy.com/flight-change-policy/ana-flight-change-policy/