If you have problems with the Apple Watch and a reset via the Watch app on iPhone does not work, there is only one thing to do: Go to an Apple store, or contact Apple Support. Because Apple Watch does not have any physical contact other than the hidden diagnostics port used by Apple engineers, it has not been possible to make a manual reset via iTunes.
Now, MFC developed a product that will make it possible. It is called Ibus and connected with a small pin to the diagnostic port. On the other hand, it has a Lightning connector to connect to the computer. So far it works only with Apple Watch Series 1.
In addition to the adapter, you need iTunes on a Mac or a Windows program developed by MFC. But the real catch is that you have to obtain system installation file (with the extension .ipsw), as Apple does not provide the same way as the files for IOS.
MFC has links to download some versions, but these only work as while Apple signs the version in question.