Copying from 1 staff to voice 2 of another staff.

Let's say I have three staves. All three are trumpet parts, trumpets 1-3. I want to combine staves 2 and 3, because the 2nd and 3rd trumpet parts aren't different enough to need seperate staves. Is there a way I can copy all the notes from the 3rd trumpet staff, and paste it into the 2nd trumpet staff as voice 2?

I have tried a couple things with the voices menu, but I can't seem to find a way to do it myself. It's not 100% necessary, it'll just help in the process of part editing, so I'll have less parts to worry about.

Thanks.