How do you reset 'Ignored words' and 'Ignore once'

I have a very long document. During the spell check, I clicked ‘Ignore all’ and ‘Ignore once’. How can I reset it so those words are checked again?

To access this command…
Choose LibreOffice Vanilla - Preferences - Language Settings - Writing Aids.

Choose LibreOffice Vanilla

???

The answer is as difficult as the solution. I am surprised at how difficult it was not only to ask/explain this question, but even more difficult to find an answer.

Answer: LibreOffice remembers all words that you ever ‘Ignore All’ in a special dictionary called ‘List of Ignored Words [All]’. You do not need to reset words that you have only ‘Ignore Once’ since, well, you only ignored them once and there is no record.

You cannot reset the spell checker for only the currently-open document. To universally reset the spell checker:

  1. Tools > Options > Language Settings > Writing Aids
  2. In the right middle pane = ‘User-defined dictionaries:’ select ‘List of Ignored Words [All]’

Now you can press either:

  • ‘Delete’ - CAUTION: pressing this button will delete ALL words that you have ever ‘Ignore All’ for all documents, ever, and cannot be undone; OR
  • ‘Edit’ - you can edit this special dictionary, but you will have to do so one item at a time!
    -VJS

The correct solution has been suggested by the first answerer (and it was long ago). What is the purpose of duplicating it?

The first “solution” is so vague as to be utterly useless. The purpose of detailing an answer is to get a definitive solution on record for posterity.