First you need to consent to use Pre-Release features in the Hierarchy Settings Properties.
To complete this click on Administration.
Expand Site Configuration.
Click on Sites.
In the top ribbon click on Hierarchy Settings.
Next place a check by Consent to use Pre-Release features
Now navigate to Administration.
Click on Updates and Servicing.
Click on Features.
Select Run Task Sequence Step by click on the item.
Right-click the item, and select Turn on.
Now close and reopen the Configuration Manager Admin Console.
Navigate to a Task Sequence and see if the option is now available for you.
The option will be under the General option menu.