The "hole" will be a very large rubber plug. You can poke out the plug with your fingers, then cut the needed hole with any utility knife. PLEASE remember to replace the plug- I don't want to see any carbeques.
That's how I do it. There's always the option of drilling a hole, but it's a LOT of trouble, and the factory hole will hold 2 runs of 2/0 and a single each of 4 and 8 with ease