Start the Manager. Click on “File” to open the menu, then select “Open TXT file.” Open the text file you downloaded from the Gecko Codes website.
You will see a list of cheats in the left-hand column with a checkbox next to each cheat. Click the box for each cheat you want and edit any that need editing. Click “Export to GCT” (at the bottom). Save your GCT file to the “/codes/” folder on the SD card you use for Wii homebrew, creating the folder if it doesn’t already exist.
Now it's time to launch your game.