It will be in /Applications/Install macOS High Sierra.app
: For older versions where the App Store may not work, Apple hosts disk images (.dmg) for manual installation. You can find these on the official Apple Support page under the "Use a web browser for older versions" section. Combo Update Download Mac Os High Sierra 10.13.6 Dmg
Apple provides DMG-based updates, such as the macOS High Sierra 10.13.6 Combo Update , though these typically require a base version of 10.13 already installed. System Requirements It will be in /Applications/Install macOS High Sierra