Opening a page to create a new asset and submitting a value like the barcode won't work unfortunately. You either can open the URL of the "New Asset" page and manually fill in the barcode or use the asset import function. This allows you to submit asset details of multiple assets, including their barcode, in an XLS format. Instructions on how to use the asset import feature can be found
here.
Note: If you would like to scan the same assets afterwards, ensure that you are using the correct unique identifiers for your new assets. Details on how Lansweeper uniquely identifies assets can be found
here.