If you may want to clear the input field before every scanned data input, then you can set a pre-amble which will clear the input field. You do however have to make sure that the cursor is at the start of the input field when the data is scanned.
The preamble setting can be configured under
Session -> Configure -> Scanner -> Preamble.
Set the pre-amble to
IDA_ERASE_EOF (Erase to End of Field). This will clear the input field and then submit the scanned data. Please note that this IDA code will only work with IBM emulation sessions.
If you would like to achieve similar behavior with VT emulation or Browser sessions, you can use a script.