There is a small mistake, it should be "/Users//Library/Application Support/IOCoin/html5wallet.conf". Sorry about that.

Some more advice if you cannot locate the file:
- Make sure you've run the wallet one or more times already, otherwise the file/folder will not exist yet.
- Your Library folder will probably be hidden. Press shift-command-G in Finder to open the Go To Folder dialog and enter the path manually.