you need to download a couple of files in the download Odin and you also need to download the specific stock firmware for your Samsung S6 device. So you don’t really need to do anything on the phone at the moment. Because everything’s going to get wiped if for whatever reason you’re stuck in a boot loop or something like that if you tried to flash a ROM this will bring you back to stock. It will also wipe all of your data and also your internal storage will backup your pictures or text messages contacts everything like that. This will bring your phone completely back to stock completely like it was out of the box.
How you can flash the stock firmware on your Samsung Galaxy S6. Download Samsung S6 Any model ROM firmware (Stock, Custom ROM) Flash Files on this page.