The code in there would either be a reference to the hidden form element you placed on the page and put the current file name into, or it could be a reference to the recordset and file name column directly (but make sure your recordset is filtered properly).
Using a hidden form element may be the easier way to debug even though it takes more steps sometimes people fall down trying to keep the update recordset on the correct row after the update button is submitted which can make the direct recordset reference a little trickier to debug when you have issues.