Greetings @Hareesha . Are all the related tasks created as part of the playbook as well? In my mind, the natural order of operations would be that the Incident is the "parent" task and all related tasks or child tasks would be truly "worked" and closed before the Incident is ready to be closed.
However, if you have a scenario in which the Incident needs to be closed and all related tasks need to be closed you could call the Flow Designer Flow Action "Update Multiple Records" and then change the State field value.
Update Multiple Records action
I've also seen people use Business Rules that when a parent Incident is resolved, it checks for child and related records and then closes out those tasks as well using a simple GlideRecord query and the .update() method.
