I'm sure I have something, but it's a simple enough one that you should probably do it yourself so that it comes out the way you want it. Not to mention the fact that it could well be less time consuming to just create it than to change the database references. Lastly, I see you're on v7 - not too many are, and compatability might be an issue.
 
Unless you end up wanting more info, you only need one table - BKARHINV; group by Customer Code, select by date and add a subtotal by group. If you want the customer name on the report you'll need to add and link to BKARCUST.
 
If even that sounds like Greek to you, don't be afraid to ask for more help.

As far as I know the reports are all backward compatible, so you shouldn't have any trouble.