WARNING: If you load multiple accounts on a single device, you may lose access to one or more of them in the process!
1) Make sure you have installed Google Play Games from the Google Store with your correct Google Play Account.
2) Make sure you have signed in your Google Play Games account with your lost account.
3) Tap on Settings > Google Play button. The game should then show the player name of the account that is about to be loaded on the device. After verifying that it is the correct account, tap “Yes”.
1) Log into Game Center using the e-mail address that you originally connected to your account. To do this, go to your device Settings > Game Center > Apple ID.
2) Once you’re logged into the correct Game Center/Apple ID, the game will prompt a message asking you to load the correct account. If you can’t retrieve your lost account with the address you’re using now, it's probably not the right one.