Why did my mileage suddenly change on the dash?

I own a 2022 Sentra and I had around 12,000 miles on it before it suddenly changed to 8,662.9 miles on the dash when I was driving. There’s also this “A” letter next to it when I never seen or know what it indicates. Before I take it to the dealership I want to know what you guys think

https://preview.redd.it/heezuftqmt7e1.jpg?width=3049&format=pjpg&auto=webp&s=fb741052be60ae128a049d34b4fa68d4b26d9818

https://preview.redd.it/4rmsnftqmt7e1.jpg?width=4624&format=pjpg&auto=webp&s=372e0ef054d452c619af523dca6ef80bad79d069