Adding a voice part to appear above the score I have already completed

I have just purchased Musescore and am using it to quickly transpose music. Not being familiar with it yet I have completed a piece and neglected to add a vocal line on top. Now when I try to add "voice" to the music the vocal line appears underneath the grand staff of what I previously worked on. How can I add the vocal line and get it to appear above the grand staff?

Thanks in advance.