How to transfer the date to the server with UTC + 0 having such initial data?

Question

JavaScript

There is such information:

const time = {
  beginDate: "2019-10-15",
  beginTime: "12:00",
  endDate: "2019-10-16",
  endTime: "23:59",
  timezone: "Etc/GMT-3"
};

The server uses UTC + 0, how, knowing this initial data, it is correct to transfer two dates (start and end) to the server, i.e. convert them to UTC + 0;
That is, on the server, this date will then be used for the event trigger.

Answer 1

Etc/GMT-3 is west of Greenwinch
12:00 (GMT-3) becomes 15:00 (UTC)
23:59 (GMT-3) becomes 02:59 (UTC) the next day (2019-10-17)
also for reference:
https://en.wikipedia.org/wiki/Interchange_dateline