- Go to your app manager on your device.
- Find the Chaos Battle League app in the list and click it
- From there you will see a button called clear data/Cache
- Press the clear data one for the app specifically
- Once you have done this ensure you are signed in to your Google Play account.
When you launch the game you should be taken to your account.

If this doesn't work you will need to ensure all your Google Play services are updated as well.