The Reverse Lines item is available via the Reformat Text button on the collection toolbar and via the Format menu, except when the Recycle Bin tab is active.
This command reverses the lines in the active clip. It swaps the first line with the last line, the second line with the penultimate line, and so on. If you selected multiple lines in the clip, then only the selected lines are reversed.
See Editing Clips and Text to learn how to use AceText.