How to Flash Stock ROM on Samsung Galaxy S21 using Odin

Preparing Your Samsung Galaxy S21

• 💡 Identify your model number (e.g., SM-G991B) and bootloader version (e.g., U3) by navigating to Settings > About phone > Software information.
• ⚠️ It's crucial to turn off your phone before proceeding to the computer steps.

Downloading Essential Tools

• 💻 Visit the HardReset.Info website to download the latest Samsung USB drivers and Odin flashing tool (latest version recommended).
• ⚙️ Install the Samsung drivers on your Windows PC to ensure proper device recognition.
• 🗜️ Extract the downloaded Odin file to a designated folder on your computer.

Obtaining and Preparing Firmware

• 🌐 Go to a trusted firmware website (e.g., SamFW.com) and search for your specific Galaxy S21 model (SM-G991B).
• 🌍 Select the correct CSC code for your country to ensure compatibility.
• ⚠️ Crucially, do not download firmware with a bootloader version lower than your current one; you can only flash firmware with the same or a higher bootloader version.
• 🗜️ Extract the downloaded firmware ZIP file; this process may take several minutes.

Flashing Stock ROM with Odin

• 🚀 Run the Odin executable as administrator.
• 📂 Load the extracted firmware files into Odin by clicking the corresponding buttons (BL, AP, CP, and CSC). Use the basic CSC file, not the HOME_CSC file.
• 📲 To enter Download Mode, power off your phone, then hold Volume Down and Volume Up buttons simultaneously and plug in the USB-C cable.
• 👍 Confirm by pressing Volume Up on the phone screen.
• 🔌 Connect your phone to the PC and wait for Odin to recognize it (an "Added!!" message will appear).
• ▶️ Click the "Start" button in Odin to begin the flashing process; do not unplug the cable during this time.
• ✅ Once flashing is complete, Odin will show "PASS!". Your phone will restart automatically.
• ⏳ Allow the phone to boot up completely, which may take some time, and then proceed with the initial setup.