For a scenario where your Android Keystore has been lost or compromised, the recommended next step will be to regenerate your Keystore.
The Play Console Help Center has guidance for this topic. For a quick reference, here is that information:
If you’ve lost your private upload key or it’s been compromised, you can create a new one. Your developer account owner can then initiate a key reset in Play Console.
After our support team registers the new upload key, the account owner and global admins will receive an Inbox message and email with further information. You can then update your keystores and register your key with API providers.
The account owner can also cancel the reset request in Play Console.
Important: Resetting your upload key doesn’t affect the app signing key that Google Play uses to re-sign APKs before delivering them to users.