The Trim Whitespace from Paragraphs item is available via the Reformat Text button on the collection toolbar, except when the Recycle Bin tab is active.
Select the Trim Whitespace from Paragraphs command or press Shift+Ctrl+T on the keyboard to remove any whitespace from the start and the end of each paragraph in the active clip's text. Spaces and tabs are considered whitespace.
If you captured some text that is indented, use Trim Whitespace from Paragraphs to remove all the indentation. If you want to unindent the text only one or a few steps, preserving remaining indentation, select the text and then press Shift+Tab on the keyboard.
To remove empty paragraphs from the start and the end of the clip, use Trim Whitespace in addition to or instead of Trim Whitespace from Paragraphs.
See Editing Clips and Text to learn how to use AceText.