Just add some ballvalves [ which you must have now on the manifold?] and adjust the flow to the cool areas over a few days until you get what you want.
You could raise the water temp a bit and reduce flow to the warm areas, pushing more water into the cool zones.
I have 6 zones, and fiddled with them for a week or so until everything got close to what was wanted. Some zones I leave full off or on if it gets extremely cold.