How to change React-Hook-Form defaultValue with useEffect()?

@tam answer is halfway through what is needed to make it work with version 6.8.3.

You need to provide the default value but also to useEffect to reset. That particular distinction is required if you have a form that you reload with another entity. I have a complete example in CodeSanbox here.

In a nutshell:
You need to define your defaultValues in the userForm.

 const { register, reset, handleSubmit } = useForm({
    defaultValues: useMemo(() => {
      return props.user;
    }, [props])
  });

Then you need to listen to potential change.

  useEffect(() => {
    reset(props.user);
  }, [props.user]);

The example in the Code Sandbox allows swapping between two users and have the form change its values.