How to override print.tpl.php from Printer-friendly pages (https://backdropcms.org/project/print).
already create print.tpl.php at
- /themes/lumi/templates/print.tpl.php
- /themes/lumi/print.tpl.ph
- clear all cache
print.tpl.php, still read from original at /modules/print/
Then you should contact the support! as I cant help you further in it. Hope this issue of yours get resolved soon!