Welcome to WikiTree and G2G, Anonymous! Have you seen this profile?
https://www.wikitree.com/wiki/Chalmers-773
It seems to be for the right Jack Chalmers, but doesn't mention the George Cross. You might like to leave a comment on the profile, at the POST NEW COMMENT link, to contact the profile manager.
Also, to do more on WikiTree, it's worth thinking about upgrading your membership (it's absolutely free). See
https://www.wikitree.com/wiki/Help:Membership