If an user task completed in the process but I again want to go for it to complete. How will I do that?
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You would have to instantiate a new instance of that task. It could be as simple as right clicking on the task and doing "Start" but really hard to say without more details.
Maybe this can help:
I also made it quick task but I am not able view the content of the form of user input task.
A quick task probably has a different meaning than you might expect.
What actual problem are you trying to solve here?