Since Light is the aspect of knowledge and information and heir is a part of the know/change pair, I thought that the Heir of Light would be able to locate a session and "contact" it's players (manipulation of information). Maybe a Page of Space could help them for this task ? I'm asking this for a little story, so I have a limited choice of god tier.

Light is Information, yes, but I don’t feel Information is something that really relates to inter-dimensional contact. Rather, it relates to Facts and more ‘written in a book and explaining things about something’ kind of Information. If you’re going for the Page, it depends- The Page of Space, being ‘served Space’, I could imagine that’d be like, being offered another whole Session to go to, which would make them being the ones being contacted rather than the other way around.