Nice site!
I think you got some things mixed up a little cause neither of the 2 sites really work :/
You have 2 domains: "themobiusstrip.fr" and "rblt.fr".
themobiusstrip.fr is the old domain, so let's assume your website works when ppl go on that domain. (Which it doesn't right now)
You can configure the domain "rblt.fr" so that it redirects to "themobiusstrip.fr". Which means in the browser address bar you will then see "themobiusstrip.fr".
OR
You use a plugin like "Wp Migrate DB" to change your database so all "themobiusstrip.fr" addresses become "rblt.fr" addresses. Then you configure your domain "themobiusstrip.fr" to always redirect to "rblt.fr" so that only the domain name "rblt.fr" will be visible on the browser address bar.