Assuming you are using the NP mixer and not the Dorico mixer, this will only set a base level for each instrument. Beyond that, one has to apply dynamic expressions within the music itself or use the CC lanes to affect changes in dynamics.
One can, by using IRV and different voices, set different volumes for different voices by confirming dynamic changes in the voice using ALT/OPT + ENTER to exit the popover.
Accordion.dorico (969.0 KB)