Do a Save As, delete everything you don't want, and reformat as needed.

If you are familiar with Manage Parts, you can create a linked part for Piano/Vocal and include just the staves you want. Then format and print the linked part.

If neither suggestion works for you, we need to know the important stuff like the Finale version, OS etc.

It's a good idea to add that to your MM Profile. That way, it appears with every post and no one has to guess.