Apple watch
My son has an apple watch that we can't remember the password to the id for and the phone number is not ours, plus it will not stay charge.
If the Apple ID is not his then there is nothing can be done except recycle it. The watch is activation locked.
Further information can be found here About Activation Lock on your Apple Watch - Apple Support
If the ID is genuinely his, Try the steps in this knowledge base article if you forgot your Apple ID Password
If you forgot your Apple ID password - Apple Support