Right-click the asset in CM, then select Open - Edit Config File Text. It should pop-up in Notepad. If you want to use something like Notepad++, then right-click the asset and select Open - Show in Explorer. The folder for the asset will open and you can find the config.text file there. If you change anything in the file, then save and exit, then right-click the asset and select "Submit Edits". If you don't want to change anything, close the file and don't save, then right-click the asset and select "revert to original"