I am not sure if this would be helpful but yesterday I was at the Mi Service Centre to have my IF earphone fixed but the procedure is the same with the phone.
1) make sure that you do regular backups as I seen that those who had issues with their phones will most likely have their motherboard replaced and their data wiped. If you do either the Mi Cloud backup or just copying the data files to an external source, be it your computer, thumbdrive or SD card, you can restore them once you get your phone back.
2) Don't throw the packing list which come with your packaging away. I know that they can scan the barcode in the phone to retrieve your data but having the packing list helps speed up the process as they just need to scan in the number on the list. Since there is no barcode on the earphones, the packing list is very much needed.
They will ask you where you get the phone from if you do not have the packing list. If you get them from the official telcos, your details may not be in their database and in which case, you will have to bring the telco receipts for the phone. Other non official sources will not be entertained.
3) They will basically just ask you to verify your name and the phone number you use to place the order. They will use that same number to contact you to pick up your phone. From what I can overhear, it will typically take between 2 to 3 hours to get your phone fix. They will contact you when it is ready. Of course, you can do your pick up the next day.
The Central is a confusing building at least for me and took me a while to find it. Basically the service centre (#04-89D) is hidden away from the public view in the Blue Sector facing the Clarke Quay.
I see that they also do have stock for the screen protectors, back covers and some MI souvenirs on the racks but I am not sure if they are available for sale.
They do servicing for MI, Oppo and Lenovo but it was a good thing that when I was there, there was less than 10 people before me and 2 of them were there to collect their phones.
Those who got the phones from out of Singapore could not get their phone serviced there and was told to go back to the seller. There was one who happened to have a "fake" redmi phone and was shown the real one to compare.
Hope that helps.