I have created a custom list named “K2 Workflow Tutorials” in which K2 workflow will be created to delete subsite. Please refer to my previous article to create a K2 workflow in SharePoint 2013 Online.
Go to K2 designer, drag and drop Delete Subsite step from the Sites workflow steps in the ribbon interface.
Select a site collection and then click on Next button.
Specify filters for the subsite to delete and then click on Next button.
Specify whether to use the recycle bin and then click on Finish button.
Deploy the workflow. Create a new list item in “K2 Workflow Tutorials” list with title field value as “TEST SUBSITE”. After few minutes the workflow will be completed and the subsite which has title field value “TEST SUBSITE” will be deleted.