All data on your Apple Watch will be erased if you unpair it. If you don’t have access to your iPhone, the backup may not contain the most recent information. You can connect your Apple Watch again and set it up from a backup when you’re ready.
How To ERASE APPLE WATCH! Deactivate iCloud and Unpair Tutorial Guide
How To Factory Reset your Apple Watch Series 3 – Hard Reset
Open the Settings app on your Apple Watch. Select General > Reset, then touch Erase All Content and Settings after entering your passcode. You have two choices if you have an Apple Watch with a cellular plan: Erase All or Erearn All & Keep Plan. To completely erase your watch, select Erase All
To pair your iPhone, you’ll need to disconnect it from your previous phone and then re-pair it. So, the first thing you should do is unpair and reset your Apple Watch to factory settings. The Apple Watch automatically returns to its original settings after being unconnected.
If you can’t locate the backup from your old Apple Watch, it’s possible that the new one you just bought is running an older version of watchOS. The procedure is inconvenient, but it works: set up the timepiece as a new device, update it to the most recent version of watchOS, unlink and reconnect it with your iPhone afterward.
While your Apple Watch is in pairing mode, press and hold the Digital Crown. When the Reset option appears on your watch, tap it. You may then pair your watch again after it has reset.
If your Apple Watch and iPhone are disconnected, the red phone symbol with a line through it appears on its display. You did not have to re-pair your Apple Watch; simply reconnect it. When your watch and smartphone return within range of one another, they should reconnect automatically.
The watch appearing twice implies that the data is being shown on the watch twice as much… When a watch is recognized as a new, active data source in the Health app, it is recorded separately. This does not result in double-counting of data.