To change your player name, please try the following steps:
Home screen (leftmost button at the bottom of the screen) > Profile icon (middle button at the top of the screen) > Tap your player name.
Once you change your player name, it cannot be changed again for 30 days.
Likewise, the player name you set at the beginning of playing this game cannot be changed for 30 days.
Note: If a player name is found to be inappropriate, it may be changed or your game usage may become restricted.