Have you looked through this thread - How to flash v2 what file do I use
Pay special attention to the file structure on the SD card, first format it to FAT32 (32GB or smaller card), then make sure the file in in the right place, I think some versions of instructions incorrectly said to put it in a folder, when the file should be in the root of the card named the way they say to name the folder. Not sure if they’ve been corrected or not.
When it prompts for a firmware update, does it not succeed?