Creating a another staff of music in the same part on a repeat

I have read several, lots, several explanations on how to add (in this case) 12 bars for a different melody line in the alto part on the repeat. I have created the second Alto Line (although I had to convert it from bass to treble clef), added the music but cannot get the playback to play the top line the first time and the bottom line the second time PLUS on the printed music to print a sing alto part with the dropdown for the 12 measures on the repeat. Hop this makes sense---by the way I LOVE Musescore!

Thanks