I always thought the Cooper's OS lager needed some hops. And since it uses an ale yeast,it's actually a light colored pale ale. 2oz of English hops would be good. You could make a 15 minute tea with the hops at the begining of the boil for 15 minutes. Then remove the hops & add your fermentables off the heat. You never boil pre-hopped extracts. Then chill & top off in the fermenter & stir or shake to combine before testing & pitching.
Ot you could look at my recipes for how I use their cans with plain DME & hops to make them better.
I put them in the BK with the usual 2.5-3 gallons of water for the partial boil. Boil the hops for 15 minutes,remove. Then take the kettle off the heat to add the Cooper's can & other fermentables. Stir well to completely mix them. Then chill in the sink in an ice bath. Add to fermenter & top off with cold water to total volume for the batch.