I created an index page. Then selected some text and told LibreOffice writer to index all similar entries. I then entered some manually by typing the entry into the dialog box. I made a typo! Since there is no matching text in the document, I can’t correct to delete the text. How do I delete the entry from the index? Deleting the index and recreating it doesn’t help.
The Alphabetic Index is only a by-product of index entry collection. Deleting it does not affect the entries interspersed in the text.
Make sure you have View>Field Shadings enabled so that you have visual clues about meta-information markup in your text.
Index entries will show as light gray background under “long” sequences marked for index or as a gray vertical bar for “spot” entries. You can right-click on such a gray background and Index Entry. It does not really matter whether you right-click on the target index marking or not because the dialog will display heavy black arrows allowing you to navigate to previous/next entry. Of course, it is better to be in the vicinity of your target. It is usually difficult to select a “spot” entry.
Note that if the entry is flagged by the spellchecker, Index Entry will not be offered because spell checking has precedence over index entry edit. Fix spelling first or silence spell checking togglinf Tools>Automatic Spell Checking or Shift+F7.