Hello roboli,
It sounds as if you are having an issue with Activation Lock.
Most likely you are going to need to reset the password of the Apple ID that is appearing on the Apple Watch. If you no longer have access to that Apple ID, these steps from How to remove Activation Lock - Apple Support should help:
Remove Activation Lock on the device
Follow the onscreen steps to enter the Apple ID and password you used to set up your device or your device passcode.
Learn how to find your Apple ID or reset your Apple ID password.
Remove Activation Lock on the web if a device is offline
1. Go to www.iCloud.com/find.
2. Sign in with your Apple ID and password.
3. At the top, click All Devices.
4. Select the device that you want to remove from iCloud.
5. Click Remove from Account.
Start a support request
If you need help removing Activation Lock and have proof of purchase documentation, you can start an Activation Lock support request.
If you are still unable to access that Apple ID, the last link in that information should help.
Have a good day.