Hi @iabukhdair,
The gantt has the built-in str_to_date method, but it will work only if you will substring the T symbol from your server output, here is an example: http://snippet.dhtmlx.com/f4bd9200a
Also, you can create the date object from this string using the default Javascript date constructor: var dateFromStr = new Date("2020-03-13T12:00:00+00:00")
After that, you will be able to format this date object using a gantt built-in method date_to_str.
Here is an example(open the console): http://snippet.dhtmlx.com/5609af6ee