Symptoms

How to terminate existing workflow running on one particular item
 

Diagnoses

NA
 

Resolution

The only way to stop a workflow is through K2 Management > Workflow Server andgt Workflows > Your Workflow name. This will list the instances from which you can select and stop them. To identify the particular one you want to stop you need to know the Folio or process instance ID. To get this info will depend on the solution design, If you used something specific in the folio to identify it you can use that, the alternative is you need to view the ViewFlow of the instance against the List item and note the URL ProcessID.

I also logged a feature request for the ability to Manage a specific items instances from the context menu > K2 Workflow > workflow History page.