If your DMG file contains the official installer app, move the app to your Applications folder and follow these steps: Connect a USB flash drive (minimum 16GB) to your Mac.
(This only works on Macs running 10.11 or newer)
Select using the arrow keys and press Enter.
The file will download directly into your /Applications folder as Install macOS High Sierra.app . Method B: Trusted Public Archives
macOS High Sierra 10.13.6 is a popular operating system for Mac computers, released by Apple in 2017. It is the 14th major release of the macOS series and is known for its stability, security, and performance. This update includes various improvements and bug fixes, making it a reliable choice for Mac users.
Download and install (runs on a free 15-day trial).