// main aware of sub form
function MainForm() {
  const { register, handleSubmit, getValues. reset } = useForm();
  const handleSubFormSubmit = data => {
    // do you submission here
    // then reset
    const { name } = getValues({ nest: true });
    const subForm = {
      other: "",
    };
    reset({
      name,
      ...subForm
    })
  };
  return (
    <form onSubmit={handleSubmit(console.log)}>
      <input name="name" ref={register} />
      <SubForm onSubmit={handleSubFormSubmit} />
    </form>
  );
}