You'll need to create an install USB Thumb drive following these instructions: [https://www.macworld.com/article/2981585/operating-systems/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html|How to make a bootable OS X 10.11 El Capitan installer drive]
The installer won't work without being mounted from a different drive or partition that is Mac OS-X/macOS.
But before you go down this path how about telling us a bit more on why you think you need to install the OS.