You have your Facebook promotion setup but now you want to change a post from one day to another. Not a problem with the drag & drop feature! You can drag and drop a post from one day to another on the open drawer of the original post and dragging it to any other day you want.
In order to get started, you will want to be on the Calendar view of your Social Posts:
Once you select Calendar, your view should look like this:
If you click on the date you want to move, you will see a drawer open up like this:
You will then want to click on the post in this drawer and drag it on over to the new date.
You will see that my post from March 10th is now on March 12th!