This is used to diagnose the workflow with error. You can access the processing of workflows with errors navigating to this path: Tools → Business Workflow → Administration → Workflow Runtime → Diagnosis of Workflows with Errors.
You can use T-code: SWI2_DIAG (Diagnosis of Workflows with Errors) - which is defined as the standard SAP code available within R/3 SAP systems depending on your version and release.
You have to enter the selection criteria as shown in the following screenshot and it will show you the list of all workflows with error.
To use this transaction, select the workflow with the error, and find out the workitem number that contains the error.
Click “Change the workitem” and make changes to the workitem with error and “Save”.