You can get the value returned by the barcode scanner using this:
First(BarcodeReader1.Barcodes).Value
Then you can use a simple lookup function to get the name of relevant room to put it in the text box. Put this in the text property of your control:
Lookup(YourSharePoinrList, RoomID = First(BarcodeReader1.Barcodes).Value).RoomName
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