Crie controlador de usuário

const createUser = async (req, res) => {
  const { email } = req.body;
  const existUser = await User.findOne({ email });

  if (existUser) {
    const error = new Error("Usuario ya existe");
    return res.json({ msg: error.message });
  }

  try {
    const newUser = new User(req.body);

    newUser.token = generadeIdToken();

    const saveUser = await newUser.save();

    res.json(saveUser);
  } catch (error) {
    console.log(error);
  }
};
Alejandro Miranda Rodríguez