It's done in actions #1 and #4.
Action #1 adjusts 3 tag fields at once: everything in front of the opening parentheses ( is kept in field TITLE), everything between (feat.) and the closing parentheses is moved to field FEATARTIST) and everything from within the square brackets [...] is moved to field MIXARTIST.
The contents of field MIXARTIST are reused in action #3 (you wanted to have both Dawin and Remix in the TITLE field.
Finally, in action #4, field MIXARTIST is split into MIXARTIST and SUBTITLE. Splitting is performed in action Import Tag Field by using the same placeholder in both Source format and Formatstring (also, see documentation),