Move Regex Groups

I've got a regex

Field: artist
Regular Expression: (Featuring:\s|featuring.|featuring|feat.|feat|ft.|ft)
Replace Matches With: Featuring: (there's a space after the colon)

and it works great, it matches all forms of feat, and I've got another one: ([^\r\t]*)(Featuring:\s) ([^\r])

that creates three groups, the first is for the artist, the second is Featuring: , and the third is what follows the featuring part, but I don't know how to put the first group in the artist tag, delete the second group, and put the third group in the %composer% tag, how do I do this?

I tried variations of $1 %artist% $2 NULL $3 %composer%, and none of them work.

A replace action does not transfer data to other fields.
You need an action of the type "Import fields (Guess values", I think.
Check the source data and then devise a guessing pattern where you enter the name of target field, e.g.
%artist% - %dummy% - %composer%

It works best with unique separators between the mask elements.