What have you got in the tag fields?
If they are filled the way you like it, rename the files from the tags with the function
Convert>Tag-Filename and probably this pattern:
%artist% - %title%
If you have nothing or not all the information from the filename in one of the tag fields, I would save the data in the fields first and then rename the files.
Use Convert>Filename - Tag
'['%genre%']'%artist% - %title%