The slow approach would be to add system breaks wherever you want Dorico to break the systems, making use of their “Wait for Next System Break” property where you want Dorico to squeeze more bars on a system. Make Into System achieves the same result but can sometimes give unpredictable results if there are already Frame or System Breaks present in the material.
My preferred approach is to insert a pair of Note Spacing Changes (from the Engrave menu). Note Spacing Changes apply as far as the next Note Spacing Change, so you might want to put a Note Spacing Change at the top of the next page, first, and set the top number in there (space for a quarter/crotchet) to Reset. Then add a Note Spacing Change at the top of the previous page - the page you’re describing - and set that top number to something smaller if you want more bars per system, or larger if you want fewer bars per system.