There are two ways that you can remove due dates that have been set for Items.
Here's how you can remove them directly from the Item:
1. Go to your Item and select workflow
2. Select the due date
3. Remove due date
This will immediately remove the due date for that workflow stage. User will not be notified of this update.
Here's how you can remove due dates from multiple Items:
1. Go to your Content tab
2. Select Items and then select set a due date action
3. Select due date
Select the due date for any of the workflow steps.
4. Select remove date
This will immediately remove the due date for this workflow stage for all of the selected Items. User will not be notified of this update.