Every time you install ConfigMgr, the setup files would connect to the internet to get update files for the setup however, internet connections may not be possible for some situation. So here is a guide to pre-download the update files for the setup on a system with an internet connection.
There are 2 ways to download the updated files
Option 1 - Run Setup Downloader with the user interface
1) Windows Explorer, and go to <ConfigMgrInstallationMedia>\SMSSETUP\BIN\X64.
2) Double-click Setupdl.exe.
3) Specify the location where the files would be stored and click Download
4) The prompt will close once the download has completed
Option 2 - Run Setup Downloader from a command prompt
1) Launch Command Prompt and change directory to the Drive letter where the CM ISO is mounted or Setup Files are located
2) run setupdl.exe with the path to where the updated files will be stored
3)The prompt will close once the download has completed
4) You can verify the contents by running the command
setupdl.exe /VERIFY C:\Users\Robinson\Desktop\SCCMUpdate
Once verification is complete the window will close.
After the download is complete you can copy the files to your target server and run the installation and selecting the Use previously downloaded files option.