First head to financial > unpaid and filter the list down to all the accounts you want to send to collections using the filters on the right. Don't forget the "more options" button on the filters if you want to real dial in your list.
Next, hit the "export" button on the right. This is the file to send to the collections company.
Last, to keep track of which invoices you've sent for collections. Select all the invoices in the list by clicking the check boxes on the left and then hit "send to collections"
