I think you need to look at the QoS rules config; I was used to ProCurve and other switches and Meraki seems to centralize this much more than others.
In the dashboard go to
Switch - Configure - Switch settings
and scroll down to the Quality of Service settings.
There is a default rule there that will trust incoming DSCP settings and a link that will allow you to customize the DSCP to Class of Service mapping, and set up your own specific rules based on IPs or ports (with some limitations on the smallest switches).
Basic docs on this are here