Program RSDRD_DELETE_FACTS will be useful for automation of this step. Please see the link.
Do you want to delete it request wise or some field wise.
If you want to delete request wise Please check below blog
Instead of WDSO you can use your cube and DSO name to get same functionality .
The blog is deletion based on timestamp .you can see comments for deletion based on request number .
Hope this will be helpful .
Since you wish to automate the selective deletion step, I think the below article will be very helpful-
Hope this helps.