in the mixer view look at the buttons at the bottom, there is one called Del. highlight any midi tracks you do not want to have volume settings and click that and then click yes. For the most part this removes existing volume settings and allow free mixing. If that does not work you have to go into the midi event list and do it track at a time as Mac said.

HP Win 11 12 gig ram, Mac mini Sonoma with 16 gig of ram, BiaB 2025, Realband, Reaper 7, Harrison Mixbus 9 32c , Melodyne 5 editor, Presonus Audiobox 1818VSL, Presonus control app.