This option is about Sharepoint OOB Workflows, it never was a Nintex Workflow option. Anyway you have some alternatives to do it on Nintex Workflow depeding on how you have done your design.
thanks for your reply. Could you give me a hint, how I can implement the function in a simple approval workflow?
Scenario: I ask my line manager for an approval, but now he is ill. Now I want to change the approver to his deputy, because he is ill, he has no chance to delegate by himself.
You can go to the Workflow Status link on the item you want to delegate.
Then click on the created task.
Then click on the delegate link
It's a design decision. You should design your workflow with the alternatives you think that could happen.
Some alternatives are:
-Wait some time and then if the task is not completed autocomplete the task with a specific outcome:
-Return to initator
-Run parallel tasks to the current approver and the initiator