Its very simple. Either use the DatabaseExplorer in RadarBox or any other external SQL Browser to open the routes database.
E.g File -> Database Explorer -> Choose routes table
Click add record and enter the details
FN = Flight Number
NO = Origin
ND = Destination
NV = Enter if you has a leg such e.g KJFK - EGLL - EHAM
CH = Enter date in sql time format (you should have other above that you can copy)
Make sure the airports are 4 letter codes.