It depends on how your system is currently reading the configuration file.
If you created a config.pro file and it resides in a custom location, you can edit this file with a text editor.
You would add a line "graphics win32_gdi"
This config.pro file is read from the folder your Creo shortcut points to. You can see where this is when you right-click the Creo shortcut and select Properties. Start-in is in the shortcut tab.
If you are creating a new config.pro file, be sure the file doesn't get a hidden .txt extension added.