This Google Apps Script project will allow your existing contacts to update their Google Contacts entries using a simple online form. The HTML form is published using Apps Script’s HtmlService.

function go() {
  var emailNAME = ScriptProperties.getProperty('NAME');
  var googleGROUP = ContactsApp.getContactGroup(ScriptProperties.getProperty('GROUP'));

  if (googleGROUP) {
    var emailSUBJECT = 'Your contact information';
    var myContacts = googleGROUP.getContacts();

    for (i = 0; i < myContacts.length; i++) {
      var email = myContacts[i].getPrimaryEmail();
      var ID = myContacts[i].getId();
      ID = ID.substr(ID.lastIndexOf('/') + 1);

      var emailBody =
        'Hi,<br /><br />' +
        'Would you please take a moment and update your contact information in my address book. <br /><br />' +
        "Please <a href='" +
        ScriptApp.getService().getUrl() +
        '?' +
        Utilities.base64Encode(ID + '#' + email) +
        "'>click here</a> and fill-in the required details." +
        'Your information will be directly added to my Google Contacts.' +
        '<br /><br />Thanks,<br />' +
        emailNAME;

      var emailTEXT =
        'Hi,\n\n' +
        'Would you please take a moment and update your contact information in my address book. \n\n' +
        ScriptApp.getService().getUrl() +
        '?' +
        Utilities.base64Encode(ID + '#' + email) +
        '\n\nJust click the URL, fill-in the form and your details will be directly added to my Google Contacts.' +
        '\n\nThanks,\n' +
        emailNAME;

      GmailApp.sendEmail(email, emailSUBJECT, emailTEXT, {
        htmlBody: emailBody,
        name: emailNAME,
      });
    }
  }
}

function doGet() {
  var html = HtmlService.createTemplateFromFile('form').evaluate();
  html.setTitle('Google Contacts - Digital Inspiration');
  return html;
}

function labnolGetContact(q) {
  var contact = {};
  contact.FOUND = 0;

  try {
    var id = Utilities.base64Decode(q);
    var email = '';

    for (var i = 0; i < id.length; i++) {
      email += String.fromCharCode(id[i]);
    }

    var contactID = email.substr(0, email.indexOf('#'));
    email = email.substr(email.indexOf('#') + 1);

    var c = ContactsApp.getContact(email);

    if (c) {
      var originalID = c.getId();
      originalID = originalID.substr(originalID.lastIndexOf('/') + 1);

      if (contactID != originalID) return contact;

      contact.FOUND = 1;

      if (c.getFullName().length) contact.FULL_NAME = c.getFullName();

      if (c.getEmails(ContactsApp.Field.HOME_EMAIL).length)
        contact.HOME_EMAIL = c.getEmails(ContactsApp.Field.HOME_EMAIL)[0].getAddress();

      if (c.getAddresses(ContactsApp.Field.HOME_ADDRESS).length) {
        contact.HOME_ADDRESS = c.getAddresses(ContactsApp.Field.HOME_ADDRESS)[0].getAddress();
        contact.HOME_ADDRESS = contact.HOME_ADDRESS.replace(/\n/g, ', ');
      }

      if (c.getPhones(ContactsApp.Field.MOBILE_PHONE).length)
        contact.MOBILE_PHONE = c.getPhones(ContactsApp.Field.MOBILE_PHONE)[0].getPhoneNumber();

      if (c.getIMs(ContactsApp.Field.SKYPE).length) contact.SKYPE = c.getIMs(ContactsApp.Field.SKYPE)[0].getAddress();

      if (c.getUrls(ContactsApp.Field.BLOG).length) contact.BLOG = c.getUrls(ContactsApp.Field.BLOG)[0].getAddress();

      if (c.getDates(ContactsApp.Field.BIRTHDAY).length) {
        var months = [
          0,
          ContactsApp.Month.JANUARY,
          ContactsApp.Month.FEBRUARY,
          ContactsApp.Month.MARCH,
          ContactsApp.Month.APRIL,
          ContactsApp.Month.MAY,
          ContactsApp.Month.JUNE,
          ContactsApp.Month.JULY,
          ContactsApp.Month.AUGUST,
          ContactsApp.Month.SEPTEMBER,
          ContactsApp.Month.OCTOBER,
          ContactsApp.Month.NOVEMBER,
          ContactsApp.Month.DECEMBER,
        ];

        contact.BIRTHDAY =
          months.indexOf(c.getDates(ContactsApp.Field.BIRTHDAY)[0].getMonth().toString()) +
          '/' +
          c.getDates(ContactsApp.Field.BIRTHDAY)[0].getDay() +
          '/' +
          c.getDates(ContactsApp.Field.BIRTHDAY)[0].getYear();
      }
    }

    return contact;
  } catch (e) {
    return contact;
  }
}