My visa in Macau will expire in Aug 23..If I exit Macau and go to HK..Is it possible to be extended?

If you want to stay in Macau longer than the permitted stay duration, you should apply for visa extension at the Exit-Entry Department of Macau Public Security Police Bureau before Aug 23, the visa can be extended 90 days at most.

You don't need exit Macau and go to Hong Kong for visa extension.