I booked the hotel check-in time with Meituan, and I filled it in today, but the hotel said it was a prompt message that the reservation was successful the day after tomorrow.

Did you fill in the departure time as the registration time? If you are sure that you are right, then communicate with the group first, ask which agent booked it for you, and let the group and the agent coordinate to check out.

If you can't, you should go directly to the hotel reservation department or the sales department, explain your reasons and ask them for help. Unless it is the golden week, it will generally be approved.