Hi Shaza - Welcome to the Atlassian Community!
Unfortunately, once a work item has been deleted, it cannot be brought back. As you can see, it is not a good practice to delete work items because of this. I suggest you modify your workflow to add a status for Cancelled or Abandoned or something like that. Then move the work items to those statuses when not needed - even if it is a mistake. And be sure to modify the Permission Scheme to remove access to delete work items for all users.
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