Drag'n drop of Gantt bars to adjust planning dates
First, enable edit-mode by clicking on the pencil on the top right. Then move the mouse over a gantt bar:
within the bar, you can drag'n drop the whole bar left/right into the past/future keeping the duration in working days
on the left side of the bar, you use drag'n drop to extend or reduce the duration by adjusting the planned start date
on the right side of the bar, you use drag'n drop to adjust the planned end date accordingly
All depending issues as well as subtasks are re-scheduled automatically, if you have enabled "re-scheduling" within the add-on's global configuration (which is the default).
You need to have schedule-issue permissions in order to modify planning dates by drag'n drop of gantt bars or shifting of planned start/end dates.