If you've just downloaded the game or you were logged out, you first need to progress through the game tutorial to the point where you can access the main menu. Then go to the Account section > "Log in."
On the starting screen, select the "Login" option.
Select whichever login method you used before:
For an email address, enter your credentials or use a one-time password to log in to the account.
For a Facebook profile, enter your Facebook profile credentials or choose the profile you used before.
For a Google account, enter your Google profile credentials or choose the profile you used before.
For Apple Game Center, select the profile you wish to use for logging in. Enter the profile credentials, if necessary.
If you used to play on an Android device with Google Play, you'll need to link it to another available login method first (an email address, a Facebook profile, or a Google profile). Find out how to do so here:
If you've been using a guest account, you'll need to link it to one of the available login methods. Find out how to do so here:
After that, you will be able to log in to your account on any device.