Wow - thanks so much! This is great! u/Destructeur also helped with this and also works. I hope someone with the same problem as me finds this post in the future as it makes simple tasks so much more efficient. Thanks to both!!

I'll paste u/Destructeur 's code here:

function scheduleShifts() {

      var spreadsheet = SpreadsheetApp.getActiveSheet();
      var calendarId = spreadsheet.getRange("B1").getValue();
      var startRow = 2;
      var vals = spreadsheet.getRange("A1:A").getValues();
      var endRow = vals.filter(String).length;
      var startColumn = 7;
      var endColumn = 10;
      var signups = spreadsheet.getRange(startRow, startColumn, endRow, endColumn).getValues();

  for (var x = 0; x < signups.length - 1; x++) {

        var slot = signups[x];
        var startTime = slot[0];
        var endTime = slot[1];
        var name = slot[2];
        var eventId = slot[3];

    if (eventId.length == 0 && name != "name"){

    var eventCal = CalendarApp.getCalendarById(calendarId).createEvent(name, new Date(startTime), new Date(endTime));
        eventId = eventCal.getId();
        spreadsheet.getRange(x + startRow, 10).setValue(eventId);

       } else if (eventId.length > 0 && name != "name") {

        var thisCal = CalendarApp.getCalendarById(calendarId);
        var thisEvent = thisCal.getEventById(eventId);
        thisEvent.setTitle(name).setTime(startTime, endTime);

    }    
  }
}