Update Event Start and End when custom date field updated

Update Event Start and End when custom date field updated

I've added a custom function that creates an Event when a date is entered.  

I need to create another function that updates said Event when the date is changed. 

Can someone please help me with a function to change the already Created Event and have it update the Start_Date and End_Date?  The code I use to create the event is below. 


If you are using code:
1. change <Walk_through_Date_Time> with your own date field. 
2. Select Edit Arguments and do -  dealId = Deals Id or Potentials Id 
  2. DealDetails = zoho.crm.getRecordById("Deals",dealId);
  3. //info DealDetails;
  4. startdate = ifnull(DealDetails.get("Walk_through_Date_Time"),"").tostring();
  5. newend = startdate.left(14) + "59" + startdate.right(9);
  6. enddate = newend;
  7. eventmap = Map();
  8. eventmap.put("Event_Title",ifnull(DealDetails.get("Deal_Name"),""));
  9. eventmap.put("Who_Id",ifnull(DealDetails.get("Contact_Name"),"").get("id"));
  10. eventmap.put("Owner",ifnull(DealDetails.get("Owner"),"").get("id"));
  11. eventmap.put("What_Id",dealId);
  12. eventmap.put("$se_module","Deals");
  13. eventmap.put("Start_DateTime",startdate);
  14. eventmap.put("End_DateTime",enddate);
  15. create1 = zoho.crm.createRecord("Events",eventmap);
  16. info eventmap;
  17. info create1;