: Hold Shift (Windows) or Option (Mac) and click Restore iPhone . Select your downloaded IPSW file.
https://github.com/libimobiledevice/libimobiledevice This is not a GUI tool. It's a command-line flash tool for Linux and macOS. Use idevicerestore to flash unsigned firmware if you have valid blobs. iphone firmware flash tool link
Best for: Open-source, command-line flashing on Linux : Hold Shift (Windows) or Option (Mac) and