Watch recycle
I want to recycle my Apple Watch, but I don’t know how to remove data. It hasn’t worked in years.
Apple Watch
If it hasn't worked in years it should not be a problem. Without your Passcode nobody would be able to access any old data . If you still have your iPhone, go to the Watch App and tap on General. Next, scroll all the way down to Reset.....tap on it and you will see "Erase Apple Watch Content and Settings" tap on it.