Customising workflow for iExpenses

Hi

I wish to make a customisation to the seeded workflow for Expenses (Internal Name = APEXP).   In doing so I hope to make a copy of the workflow top process and somehow get the workflow to start at the customised top process rather than seeded one.   So far I have been unable to determine where or how I need to direct iExpenses to the customised start process and this is what I require feedback from the community on.

In Procurement, this is achieved by configuring document types.   For account generators, there is a page where you are able to specify which start process.    Please can anyone assist me with how to achieve this in iExpenses for the APEXP workflow.