If you don’t have access to the connected iPhone, you can factory reset your Apple Watch from the settings app on the smartwatch. Here’s how to do this:

1. Open the Settings app on your Apple Watch.
2. Tap General.
3. Scroll down and tap Reset.
4. Tap Erase All Content and Settings.
5. If the Apple Watch is a cellular model, choose to keep or remove the plan.
6. Tap Erase All to confirm.

Once the Apple Watch is erased, all the saved media, data, and personal settings will be removed. However, you won’t be able to pair it with a new iPhone until Activation Lock is turned off. Here’s how to turn off Activation Lock without the connected iPhone:

1. Open the iCloud.com website and sign in with your Apple ID.
2. Click Find My.
3. Select the Apple Watch.
4. Click Remove This Device.

It’s worth noting that if you have a used Apple Watch, you’ll need to get in touch with the original owner and ask them to unpair the smartwatch using the steps above before you can set it up with a new iPhone.