Hello Zigfeld67,
Welcome to Apple Support Communities!
We want to help make sure your Apple Watch is connected as expected with your iPhone.
Have you used these steps to unpair the old watch?
"Unpair a Bluetooth accessory
To unpair a Bluetooth accessory, tap Settings > Bluetooth, find the device you want to unpair, and tap the info button
, then Forget this Device. This will remove the accessory from the list of available Bluetooth devices.
To add the Bluetooth accessory to your device again, place it back in discovery mode and repeat the steps above to pair it."
This Apple Support page has the full details: Pair a third-party Bluetooth accessory with your iPhone, iPad, or iPod touch - Apple Support
We hope this helps to remove the unneeded device.
Please let us know if you have further questions.
Cheers!