There are two different ways to edit several tasks at once:
on the three dots menu of the column. You can move, push, archive all tasks from the column.
Batch Edit on the Table view
Group tasks operation or Batch Edit is available on the Table view. You may notice the button at the bottom of the page.
Once you click on the button, there will be empty boxes near the task title. Choose a task/tasks you want to edit and choose one of the operations you need.
To ease the tasks searching you can use the Quick filters or sort tasks by swimlanes, members, labels or other columns.
Once you choose tasks from the list you will be opened the pop-up with the group tasks operations: from edit members to delete tasks - and the number of chosen tasks.
Then click on Exit Batch Edit, and the pop-up with group operations will disappear.