The Move Text into New Clip item is available via the Insert and Extract Text button on the collection toolbar, except when the Recycle Bin tab is active.
Select this item, or press Shift+Ctrl+M on the keyboard, to create a new clip, using the selected part of the text of the active clip as the text for the new clip. That selected part is then deleted from the original clip. The new clip becomes the active clip.
See Editing Clips and Text to learn how to use AceText.