Depending on which way you pass the ground (I’m assuming on Newmarket Road), if you pass the ground on your left; there is an alleyway/snicket before the Thrifty van hire place (I think it’s Thrifty anyway) and CUFC club shop/supports club end (you’ll see a few steps and then the alleway itself).
If you go down there you’ll come to the main stand entrance to the ground. I’m assuming on the day the gate that players and sponsors usually drive their cars through will be open with a person on the gate letting people in. That’s what sometimes happens for events that the main stand, and the Dion Dublin suite beneath is only being used etc
You’ll be able to see the entrance to the Dion Dublin suite from the gate but I’m sure whoever is stood at the gate will point you in the right direction anyway. Or just follow the fat blokes at this point!