Check out this video from Rick Corvette Conti which shows you how to get into your C8 Corvette if your battery is dead.
First, you need to tap on the side button on your key to get to your emergency key. Then under the side rear quarter section of the door vent.
Then you can turn the key to the right to access the car and access a manual frunk release where the battery is. Then behind the brake pedal there is a loop you will notice and you need to pull that twice to gain access to the frunk and battery area.
Corvette C8 Vehicle Access with Dead Battery
Luke Pressel, Corvette Service Specialist at Criswell Automotive, demonstrates the process of gaining entry into a locked C8 when it has a dead battery and the door will not unlock without power. Use the manual key to access and unlock the vehicle. Remember to keep your trickle charger connected this winter.