Change Instrument Sound in Mixer?

I don't usually post on the forum but I have a question - I know how to change the way different instruments sound in playback by using the mixer, but one of the instruments changes mid-score and I'm wondering how to change the playback for the new instrument, because it doesn't show up in the mixer. I'll add a picture of what I'm talking about in the score- the instrument changes from a bass to an alto voice where it says "Female Solo." I used the "Change Instrument" function in the "Text" part of the left toolbar, as you can see. I currently have the mixer set so all the "voice" parts sound as an electric piano because I hate the "Choir Aah" sound. When the instrument changes, the sound goes back to "Choir Aah" for that part and I don't know how to change it. Please help!