I have created a custom list named “K2 Workflow Tutorials” in which K2 workflow will be created to delete unique list item permissions.
Go to K2 designer, drag and drop Delete Unique List Item Permissions step from the List Item workflow steps in the ribbon interface.
Specify the list for which you have to delete unique list item permissions and then click on Finish button.
Deploy the workflow. Run the workflow for the list item which has unique permissions in “K2 Workflow Tutorials” list. After few minutes the workflow will be completed and deletes unique list item permissions.