Extract ISO Image from a macOS installer Step 1 Download macOS Installer (InstallAssistant.pkg). Here is the link to Sonoma beta installer: https://swcdn.apple.com/content/downloads/14/54/042-41491-A_WCZEM7L2US/b5eeeylcnmf82ycto51pvy0klcyzd02on8/InstallAssistant.pkg