Hello Ramya S Ramesh,
I don't think you need an entity Delegation here
What you can do is letting a Microflow change the associated user of said Task
You can do that by:
*You can add validation rules to your Microflow to prevent it from replacing the associated MyUser to another whose on vacation as well.
*You can automate the process by letting a Microflow be called whenever someone goes on a vacation.
Hope this helps!