Bricks, Masonry, Asphalt and Concrete - Cold Storage room question

I am currently finishing my basement and I ripped out the old cold storage room. There is still the hole that was cut in the concrete foundation to allow cold air in. I have finished the inside walls with wood studs, insulation and vapor barrier. The hole goes out into the garage that was added after the house was built so the hole is not exposed to any of the elements, just cold air. I realize now that I should have tackled this before finishing the inside walls. Is there a way to seal off this hole from the outside using concrete or another material? Thanks for any help.

How big is the hole? How thick is the wall?

The wall is 6-8" thick. The hole is about 5"x10".

Cut two pieces of 2 x 4 the height of the hole so they fit snug against the sides. Tap them in place about an inch and a half back from the surface. Screw a piece of sheet rock or plywood to them. Then mix some mortar and apply it. Make sure it's a little on the dry side so it stays in place.