Repair Hole in Cinder Block Foundation
Option one - toss enough mortar or hydrualic cement in the hole to fill up the core. Tedious, and annoying, but it works.
However, option 2 also works and takes a lot less material. Cut 4 strips of wire mesh or stiff screen about as wide as the widest part of the hole but longer than the hole. Tie long wires to the middle of these in pairs, arranged so that when pulled tight each pair of strips is at angles to each other. i.e. they make an X
Slack off the wires so the strips can be stacked on top of each other and slid through the hole while holding the wires. Once the strips are all the way in, pull the wires tight and tie to something outside the wall. Pack in some hydraulic cement or mortar and wait. Once that has set, you can cut off the wires and finish patching the hole. Do this from both sides (which is why you made 4 strips in sets of 2 - one set for each side.)