In PlayScore 2 you can set the instrument for each staff independently.  Try out new orchestrations and see how your music sounds with different combinations of instruments.
In PlayScore 2, instrument selection affects the sound only.  If you choose the horn for example you will hear the notes on that staff as a horn.  If a real horn player were to read the same notes the music would come out transposed – because the horn is a transposing instrument.   But in PlayScore 2, instrument selection affects sound only.  PlayScore 2 also has extensive facilities for accommodating transposing instruments which is discussed below.
From the Play screen tap the Staves icon lower left
In the section for each staff, pick an instrument
Tap Done
You might find you have to adjust the volume sliders for different combinations of instruments to make the sounds blend, or to make a solo part stand out.