Download the custom flag image files
Make sure each flag is a square PNG file
Rename the files to simple names without spaces if needed
Open CKAN
Select Kerbal Space Program 1
Go to the available mods list
Search for the flag pack or custom flag mod
Check the mod details to confirm it supports KSP 1
Select the mod and click Install
Wait for CKAN to finish installing
Launch KSP once after installation
Open the game’s Flags folder in the KSP install directory if the mod requires manual placement
Copy the flag PNG files into the Flags folder if needed
Restart KSP
Open the flag selection menu in game
Select the custom flag from the list
If the flag does not appear, verify the file format, file size, and folder location
If CKAN does not show the mod, refresh the mod list
If the mod is incompatible, install a KSP 1 version of the flag mod only