How to GET STARTED and
→ Download the latest version of the ZIP file. → Extract it into your wordpress installation directory.This should be enough. There's also a chance that the extracted file will generate a new folder called wordpress-maintenance-mode-main. Simply relocate/move all files in this folder to the wordpress installation directory in such circumstances.
→ Rename .maintenance file to .maintenance-old → If you don't see maintenance mode when you visit the site, it probably because of the cache.