@Inna22 You'll prob. never get a 5 out of them, but maybe tomorrow send them a message that explains that airbnb has recently cut staff due to COVID and they are also continuing to tweak the site, and you believe this must be what happened. Reiterate that you have never changed your check-in time of XX, and that according to how the site is configured it should have been IMPOSSIBLE for them to get a check-in time that is different from the listing.
Then you can go on to sympathize, not apologize, that you understand how stressful and upsetting it must have been to find out that airbnb had made such a mistake. Blah, blah. Now that they're in the house you hope they can finally relax and enjoy. Depending on how many days the stay is, you could drop off a $10/15 gift and a note if you think that will make a difference in getting a better review.
You should def. contact airbnb and tell them what a mess they created for you and the guests.