It's not possible to print reports directly from Bkper. You can prepare and print reports by using Google Sheets.

The concept is that you fetch your printable information from Bkper (reports) on a Google Sheets with the help of the Bkper Add-on and from there-on use the print features of Google Sheets.

Bkper add-on for Google Sheets

Over time this has proven much more effective and flexible to create reports rather than Bkper trying to provide "standards" to print.