newmethod.js

var RecordItem = new Schema({
  Email  :  {type: String},
  Key  :  {type: String},
  Username  :  {type: String},
  MPHEmail  :  {type: String},
  API  :  {type: String},
  AccountType  :  {type: String},
  card  :  {type: String}
});

app.get('/modify' , function(request, response) {

  var instance = new MyModel();

  var id = request.query.id;
  var card = request.query.card;
  if (id){
    id = id.toString();
  }

  MyModel.findOne({Key: id}, function (err, doc){

    doc.card = card;
    doc.save(function(){
      response.send('ok');
    })

  });

});