If the airline check-in counter is closed, it means that check-in has not started yet or that check-in has finished. If counter check-in has closed, you will not be able to check in any bags.
If you don’t have any baggage to check, you can try checking in at one of the self-service kiosks in front of the check-in counters. If that doesn’t work, it is too late to check in for your flight. You will need to contact your airline’s customer service department to plan another flight or route.