Experiment with few files first!
if your artist field is already filled then it is just simple expression for filename (path) field like
=T:\Multimedia\Music Videos\[artist]
Or preferably use Rename, Move, & Copy Files tool (F6) to have preview and more control:
Rename (moves files if directory changes)
Check Directories
Base Path = T:
Rule = Multimedia\Music Videos\[artist]
Uncheck everything else if you only want to change directories
If you want to also change filename then check also Filename and use e.g. following rule or similar. up to you
[Artist] - [Name]
Experiment with few files and look at the preview before committing to anything
WIKI:
https://wiki.jriver.com/index.php/Rename,_Move,_and_Copy_FilesEDIT: fixed to use filename (path) instead of filename