Help with scanning a barcode serial and transferring the scanned serial to another lookup field in Zoho Creator

I have two fields, same form: a barcode field and a lookup field. I want to scan a serial with the barcode field, and then put the serial in the lookup field, but I keep getting an error. The barcode field is a string field apparently and the lookup field is a bigint which might be the problem.

Can you help me fix my code to solve this please? I've gone over the documents and still can't figure it out. Thanks.

My code below:

Scan = row.Scan; // scan field
NewScan = Scan.remove("-"); // removing dashes from scan field wfter scan
row.Scan = NewScan; // putting the serial back into the scan field after removing the dashes
row.Device_Serial = Scan; // putting the scanned serial into another serial field, but it is not working because this field is a lookup field