How do I find my Apple TV password

If instead you meant the account sign-in, use your Apple ID credentials.

If you forgot your Apple ID password - Apple Support

Apple TV passcodes should appear on the screen of the TV the Apple TV is connected to for you to enter on the device you are trying to AirPlay from.

Apple TV passwords can be found in Settings on the Apple TV and changed or remove from there.

Settings ➜ AirPlay and HomeKit ➜ Require Password

click here ➜ If you're asked to enter an AirPlay password on Apple TV - Apple Support