To reset an Apple Watch to factory settings without a paired iPhone, follow these steps. First, ensure that your Apple Watch has sufficient battery life or connect it to a charger.

On your Apple Watch:

Go to the Home screen by pressing the Digital Crown.
Find and tap on the "Settings" app (gear icon).
Scroll down and select ""General.""

Resetting:

Scroll down and choose "Reset."
Tap on "Erase All Content and Settings."

Confirmation:

If prompted, enter your Apple Watch passcode.
Confirm your decision by selecting ""Erase All"" when asked to erase all content and settings.

Wait for Reset:

The Apple Watch will begin the reset process, erasing all data and returning to factory settings. This may take a few minutes.

Set Up as New:

Once reset, you'll see the Apple Watch welcome screen. Follow the on-screen instructions to set it up as a new device.