You could use the Converter "Filename - Tag" with the mask
%title% - %artist%
if the TITLE is fine and only the ARTIST should be filled with the data from the filename then use this mask:
%dummy% - %artist%
(there are also action to import tags from tags or to split tags into several tags - but as the converter has a preview function it may reassure you that you got the mask right)
look it:
File name is: x1 - x2 - x3_
File name is: 01 - Jah Mike - Lovers Rock
Title is: Jah Mike - Lovers Rock
I want the file name to be 01 - Loves Rock and Artist to be Jah Mike
File name: x1 - x3__ x2
File name: 01 - Loves Rock___Jah Mike
File name: %title% - %artist% - %title%