This will find the pattern you are requiring but be careful. Make sure you have the COMPOSER column shown so you can see what you are changing when you run the below action.
The use action type: Action type:Format value Field:COMPOSER Formatstring:$regexp($regexp(%composer%,'([^,]+),\s{1,2}([^,]+),*(\s{1}|$)',$2 $1 / ), / $,)
Run in batches but if you are confident that they match your requirement then do them all. Ctrl Z is your friend.