Three issue attributes can be changed on Gantt Chart by clicking the "Edit" tab:
1. Assignee
2. Start date
3. Due date
After editing, click "Edit Done" to update the data or click "Cancel" if you decide not to update the data.
To alter the task timeline easily, you can drag and drop the issue bar into the timeframe of your choice or drag the issue bar endpoints to adjust the start date and due date.