Hit reply to a post, go to the top bar, hit the ā+ā button on the very end, and then hit quote whole post:
Looks like this^
Itās a good way to see how anything is formatted and how to do it yourself! 
For example, if you do that to this post, you should be able to see that the formatting for a dividing line is three asterisks in a row on their own line. 
Works on both mobile and PC, on mobile you do have to swipe/scroll the top bar to get to the + button all the way at the end, fyi.