Native speakers sometimes talk about a “one month anniversary”. So I suppose you could wish the couple a “Happy one month anniversary”. This seems to be a contradiction though. We normally associate the word “anniversary” with events that occur every year and not every month. I don’t think there is a special way to greet someone who has been married for just 30 days. If a couple succeeds in staying together for a year, then you can wish them a “Happy Cotton Wedding Anniversary”. On this day, you are supposed to present the couple with things made of cotton.