BCM Workflow first step release Subworkflow WS31000004

Dear Experts,

I was working in BCM Workflow(WS50100024) and found that for first release step Subworkflow WS31000004 gets triggered. But i was not able to find how WS31000004 is getting called. Where exactly in configuration(SPRO) WS31000004 is maintained. We have requirement to replace WS31000004 by custom workflow template.

Thanks in Advance !

Regards,