Adding Instruments to MuseScore Drumline

I am trying to write a piece on MuseScore Drumline that requires three marimbas instead of two (which is what is given). I am trying to add another marimba manually by using Edit>>Instruments, but this isnt the same marimba format as the ones given. The ones given have another line for cymbal rolls and such. How do I add this special line? Attached is what I mean by the line.