Where is the Instrument Panel?

Really, I just want to add an instrument to an existing score. Is there a simple way to do that?

Simple way:
Press i (for instrument ;-).

On a couple of pages in the doc, it shows 3 panels on the left of the screen: Palettes, Instruments, Properties. I only have Palettes. How do I get Instruments?

Use menu item: View > Instruments
F7 will toggle the panel on/off.

I want to modify the tablature and one of the pages says to toggle F7 for the instruments panel. However, with the instruments dialog (i) showing or not showing, the F7 key does nothing.
The 3.0 manual shows an interface that's different from the instruments chooser. I've turned on all the toolbars... What am I missing?

For clarity, I want eventually to put in dulcimer tab, which is diatonic: fret 1 is a whole step above open, fret 2 is another whole step above 1, fret 3 is a half step above 2, fret 6 is scale degree 6, fret 6+ is degree 7, fret 7 is octave, fret 1+ is a minor third above open. If this is possible, I'm going to need help.