Adding screen sizes function not working

Thank you for this plug-in. Great work.

I added the screen size function to my functions.php file, but can see no change (the Galaxy tablet option does not show up). I also tried adding it to your responsive-page-tester.php file on the off chance it was meant to go there. No luck. Do I need to change the ‘mythemename_filter_rpt_sizes’ to match my theme name? I tried that too, no good. I appreciate your help. Here’s my site:

https://cee.virginia.edu/

https://www.ads-software.com/plugins/responsive-page-tester/