To update existing data in MongoDB, you use methods provided by the model.

A common method is findByIdAndUpdate.

app.put('/users/:id', async (req, res) => {
  const updatedUser = await User.findByIdAndUpdate(
    req.params.id,
    req.body,
    { new: true }
  );

  res.json(updatedUser);
});

The first argument is the id, the second is the new data, and the third option ensures the updated document is returned.

Example:

PUT '/users/123': updates user with id 123.

This allows your API to modify existing records in the database.