Public Holiday on Sunday

How to automatically set following day is public holiday when the PH fall on Sunday?

Go to Attendance->Holiday, then add 2 Jan and 24 Jan as Holiday will do. Just remark it as replacement Holiday if you wish.

ic, meaning have to set manually instead of it automatically become PH on the following day?

Yes, correct. Because some employers may not necessarily make the next day as holiday.

noted, thanks.