-x64- Setup | Ue4 Prerequisites

The command-line argument used by the Epic launcher is:

The default behavior in a packaged build is set in: Project Settings > Platforms > Windows > Prerequisites Ue4 Prerequisites -x64- Setup

C:\Program Files\Epic Games\UE_4.27\Engine\Extras\Redist\en-us\ Look for the executable named: The command-line argument used by the Epic launcher