I have issues with the event time zone in my script. I browsed through many topics like this, but my beginner's skills did not allow me to transcribe the solutions to my own case ...

Here's my script:

function book1() {
var form = FormApp.getActiveForm();
var responses = form.getResponses();
var len = responses.length;
var last = len - 1;
var items = responses[last].getItemResponses();
var email = responses[last].getRespondentEmail();
var equipment = items[1].getResponse();
var datestart = items[2].getResponse();
var dateend = items[3].getResponse();
var cal = CalendarApp.getCalendarsByName(equipment)[0];
Logger.log(datestart);
Logger.log(dateend);
var start = new Date(datestart);
var end = new Date(dateend);
Logger.log('start '+start);
Logger.log('end '+end);

var allEvents = CalendarApp.getCalendarsByName(equipment)[0].getEvents(start, end);

if (allEvents.length < 1) {
var event = cal.createEvent(equipment, start, end)
.addGuest(email);

MailApp.sendEmail({
    to: email,
    subject: "Equipment " +equipment+ " booking confirmed",
    htmlBody: "Equipment " +equipment+ " available, please return it by " +dateend+ " and scan the QR code when returning it.",
  });
}

else {
  var blob = HtmlService.createHtmlOutputFromFile("calendariframe").getBlob();
  MailApp.sendEmail({
    to: email,
    subject: "Equipment  " +equipment+ " not available",
    htmlBody: blob.getDataAsString(),
  });};

}

I can't find the right way to use getTimezoneOffset() or Utilities.formatDate in the right way. Would you have any advice on where to integrate them in my script so that the createEvent() works in GMT+1?

Thank you very much in advance for your help!