Double WF triggered when saving a held PO with changes made in it.
The question is vague... you are having troubles because 2 workflows are triggered? Or do you want 2 workflows to trigger? To see which flows are being triggered by the event, check SWEL (turn on tracing in SWELS first). Then, SWETYPV will allow you to see which events are triggering which workflows. From that table, you can edit/add/delete entries if you wish more or fewer workflows to be triggered.
Hope this helps, elaborate on your question if not...