Sprayer bypass valve PID setup

I’ve written a short code to control the rate on my sprayer.
I’ve got a mcrotrak bypass valve and flow meter but im struggling to tune the PID for the bypass valve.
For whatever reason I can’t get anything meaningful out of the IDE serial plotter so I’m left with only the monitor and serial prints to help tune the valve.
Wondering what methods others have used, and even some starting settings.