How do I lower the volume of just one instrument in the drums? I would like to lower all the volumes of the side stck only. Thank you.

Lots of way depending on what is producing the sound. 

But one way I work with this is to just highlight that one note buy clicking the left side in piano edit and then use the velocity scale and ramp it down. 

Session drummer has a mixer. 

I am trying that method but all the velocity scale show up for all the drums. When I click on show only the notes selected then select the sidestick on the left nothing shows up

I finally got ther but don't see how. New to this thing. Thank you for your help.

Lowering the velocity might not give you the exact sound you want, as this corresponds to the drummer playing softer = different timbre than lowering the actual volume.

Do you have your drums set up so you have 1 Midi track + several audio tracks (1 for kick, one for hat, snare etc?)

Yes I agree, that's true for some sounds that will change but I find if a drum part is cutting through then velocity IS what I wanted because it is the equivalent of telling the drummer to hit it softer. But yes you have to understand how it all works to squeeze sound your after out of MIDI and soft synth's. 

 An interesting part of working with a digital drum set is how velocity can radically change the timber. Like the ride will change to a bell tone above 118 vel. when using the brain, but session drummer does not. 

TFi What are you using to produce the drum sounds???