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