You can set a new password or change your current password from the game's "Settings" menu. To do this, you will need to press the tool icon on the top right-hand corner of your home screen.
Once you have done so, you will need to select your username to access the "Account" section, where you will find the "Create a new password" and "Repeat password" boxes, in which you will be able to set your password.
We invite you to visit the article: I forgot my password, how can I recover it?