Best way to scan QR codes?

Headed to a Trial by Frost prerelease tomorrow and wondering what I should do for scanning QR codes. I’ve read that the app is buggy and looks like it hasn’t been updated for awhile. But I also don’t see anywhere on the website to scan.

Related question. I have several starter decks. Should I scan the QR codes for all of those?

Also, does scanning cards give you options to play with more cards on BGA?

Anything else I should know? Before heading to the prerelease? Thanks!