Format Your SD Card

If you’re on Windows, use fat32format to format your card. Alternatively, you can use Rufus.

If you get an error message mentioning the SD Card is currently in use by another process, make sure you don’t have it open on your file browser, then hit Ctrl+Alt+Del to open the Task Manager, look for and kill the Windows Explorer process by right-clicking it and selecting End Task, then go to File > Run New Task, input "explorer.exe" in the command field and hit Enter. Then try again.

If you’re on Mac, use Disk Utility which you already have installed. Here’s specific instructions. Remember to use fat32, not exfat.
If you’re on Linux, you can use gparted to format your SD card to FAT32.

Update Your Firmware (MM+)

When upgrading your firmware there’s always a risk of bricking your device. Be sure to follow the instructions below carefully, as doing so incorrectly can heighten said risk.

A Note for Miyoo Mini (non-Plus) users: The version numbers and downloads mentioned in this section do not apply to you. For the regular Miyoo Mini, you want to be on a version starting with 20220419. If you’re not, check the Installation Instructions on the Onion wiki for next steps.

Check your Miyoo Mini Plus’ firmware version (Turn it on and go into Settings > About Device; you don’t need to have an SD inserted to do this). You want the version number to start with 20230505 or 202306. If it does, your firmware is up to date and you can skip to the next section (Install Onion).
If you need to update, download this ZIP file, grab the file that ends in .img (i.e. miyoo354_fw.img), place it in your SD card’s root directory (should be the only file on it if you’re following this guide) and insert it into your MM+.
With the device turned off, connect it to your PC through USB. This will start the update process (you should see a picture of a rocket as it occurs). Once it’s over, shut down your device, remove the SD card, insert it back into your PC and delete the .img file.

Next: Installing Onion