You can mass edit multiple tasks at the same time. You can select all tasks in a space, or specific ones, and then move to folder, add tags, change the due date, mark complete/incomplete, favorite, or delete.
Bulk edit is available from within a space on the Tasks and Files tab. When you click into the Tasks tab, click the pencil icon in the upper right under the plus (+) icon to access the bulk edit options. You can then click the checkbox at the top at the left to select all tasks or go through the list and individually select the tasks you want to affect. Once the tasks are selected, click the icon in the upper right to perform the action you are interested in. Click the folder icon to move the tasks to a specific folder, click the tag icon to add a tag or multiple tags to all the items, click the calendar icon to change the due dates for multiple tasks at once, click the check mark to complete all the designated objects, click the check mark to make incomplete multiple completed tasks, click the star to favorite all the selected tasks, and click the trash icon if you want to delete all the chosen items. You will see a notification at the top of the page after the action completes.