With respect to, can be used instead of as for. So it will be With respect to Mattie's third wish, Oprah Winfred asked Mattie to appear on her show
Or ... you can just start the sentence with "For..." and omit "As."
Instead of "As for," you can use phrases like "Regarding," "Concerning," or "In regards to." These phrases can be used to introduce a topic or provide information about a specific aspect of a conversation or situation. In the given sentence, you could use "Regarding Mattie's third wish, Oprah Winfrey asked Mattie to appear on her show."
