Simple midi channel change in part? SOLVED

SOLVED: I’ve done it using different voices, upstem 1 to one channel and upstem 2 to another, so this works perfectly for my purposes. My original question may still prove useful so happy to receive answers.

I have an old version of Miroslav Philharmonic which runs in SampleTank 3.
I’ve looked at the online Dorico manual but I’m not able to understand a simple way to do the following:

I want to be able to change midi channels during a cello part to switch from arco to pizzicato, and then back again. I’ve opened expression maps and I’m rather confused by the number of options. I’d just like to be able to insert a command at the point where the cellist play pizz to switch from Midi channel 3 to 4, having already loaded Philharmonic with legato cello on 3 and pizz on 4.

I’ve added two functions with absolute channel changes, but cannot see how to assign a command within the score to force the change.

I hope there’s a simple way to do this as I’m not really comfortable with building a huge expression map - hopefully I can upgrade to VSL or similar where these functions would already exist, but for the moment I need to make do with Miroslav.

Any advice gratefully accepted!