如何使用日期或日历更改UITextView中的值？

I have a UITextView that I need to change for the next "String" in my array every day for 2 times(every 12 hours). I have some array here that I need to use with Date and UITextView. How I need to use Calendar? My simple question is "what I need to do?"I have a UITextView that I need to change for t