If you want to override a database-backed variform for a N4 Mobile screen but do not know the variform ID, navigate to the correct form in N4 Mobile from a full web browser. Right click anywhere on the page except an image and select "View page source" or "View Source" from the drop-down menu. Search on the field name with all spaces removed. The ID attribute of the input tag for the appropriate field contains a three-part name: first the word "program" with a colon (:), then the name of the appropriate variform, followed by a hyphen (-) and the name of the specific field.
For example, to edit the Track Pos field, view the page source of Rail Inventory's Create Railcar form and find the input tag which contains the field name TrackPos: <input id="program:MRIV004-mrivNewRailcarTrackPos_input" name="program:MRIV004-mrivNewRailcarTrackPos_input" type="text" value="" size="5" onkeypress="return enterHandler(event)" />. The first portion of the input tag after the colon, MRIV004, is the name of the variform. Edit that variform in N4 to change this screen.