You can edit multiple tasks at once with the Batch edit mode.
- Open the Tasks tab in a Project,
- Click the Batch Edit button,
- Select the tasks you wish to update by checking their boxes (selecting tasks won't mark them as completed)
- You can complete the selected tasks or move them to Trash. You can also change their task list, assignee, due date, labels, visibility to Clients, and priority,
- Click Update selected tasks to apply the changes, or Exit batch edit to discard the changes.