If it is a SCID DB then you click on the [save] icon on the toolbar to save the game and then you get the [save] window in which you can edit any of the available information.
You can also click the [edit] menu and select [Paste clipboard text as PGN game]. When the [Import PGN game] window opens, click on the button [Paste Current Game] and then you can edit information there. When you are finished click the [Import] button.
Hope this helps. If it doesn't - send me a message and we'll figure it out or post something here. 
Is there any way to do this inside Scid?
I have games in a DB where the players and dates are represented by ???, and I would like to fix this information.
The best I can come up with, is export the game to pgn, edit the pgn file, delete the original, and import the edited pgn.
It just seems there should be a shorter way?