How to change your Trainer's nickname in Pokémon Go for Android
- Open Pokémon Go from your home screen or app drawer.
- Tap the red Poké Ball on the bottom of your screen.
- Tap the Settings button on the top right of your screen.
Tap Change Nickname in the Settings list.
- Tap Yes to the question "Do you want to change your nickname?"
- Enter desired nickname. Tap OK.
Tap Yes to confirm.
That's it! Now your Trainer's nickname is changed forever, and the only way you can choose a new one is to create a new account.