After you hit Reply, you’ll get the standard Reply field below the post you just read. In order to Quote that post you just read, hit the dialog bubble icon, upper left of the Reply field.
How to Quote a Post in a Reply
juliancates
#2
There’s more than one way to do it. For instance at any time you can highlight the text in the message you want to quote. A little quote button will pop up. Click it, and the quoted text gets put into your message.