You only have a limited time to edit posts. I think it is only about three days or so. I may be wrong. It has led to my personally taking a few seconds to proof my own posts. I am legally blind, so even when I miss stuff, at lest ihave an excuse.

Click on the 3 little horizontal bars in the lower right of the post, then select "edit", proceed on the screen that pops up...do not forget to hit the "submit" button at the bottom or the whole thing will disappear forever!

After awhile, the edit button disappears on my posts. It's frustrating.

This is the Edit Button on an Original Post. If it's not there - you've gone past the amount of time you had to edit it. (which is dependent on your level plus how much time has passed).

Tap the three lines next to the star on the post.