The tasks.update() method commits changes made to a DayPilot.Task using change methods such as text(newText) and start(newStart), and updates the Gantt chart.
DayPilot.Gantt.tasks.update(task)task (DayPilot.Task) - object to update
const task = gantt.tasks.find("1");
const newStart = task.start().addDays(1);
const newEnd = task.end().addDays(1);
task.start(newStart);
task.end(newEnd);
gantt.tasks.update(task);