When you refer to the "Key" I assume you mean the field labeled "Key" in the Edit Flag window. If so, that is simply a memo field which you can contain any notes about the use of the Flag. It has no actual connection to the Values available in that Flag.
If the Key is wrong, open Flag Manager, from the File menu. Select the Flag in question and click the Edit button. The field labeled "Description" is the same as the one labeled "Key" in the Edit Flag window (I have no idea why they are labeled differently). Edit the contents of the Description field to suit. You can put anything you like there - notes on what the Flag is used for, an actual key to the allowed values, or anything else.