I'm Cian, one of the Gurus here at Shopify. Thanks for getting in touch!
There is no on/off button in relation to that. 2D scanners can scan 1D and 2D barcodes.
Are you using the Shopify supported scanner? - Socket Mobile CHS 7Qi 2D barcode scanner: https://docs.shopify.com/pos/retail-package/buying-hardware/supported-shopify-pos-hardware/barcode-s...
Another thing is to make sure that you have updated to the latest version of Shopify POS.
Also, here is the link to the Shopify doc on Redeeming gift cards on Shopify POS: https://docs.shopify.com/pos/using-pos/gift-cards/redeem-gift-cards-pos
All the best!