How to propagate paragraph "Next Style" settings to existing content

How to propagate paragraph “Next Style” settings to existing content.
I have been working on converting a book to LibreOffice. I have my paragraph styles set the way I want. For example: Letter Salutation with “Next Style” Letter Text. This works fine when typing a new document. However having existing text I cannot find a way to have the Next Style applied.

In the organizer page of the Paragraph Style dialogue box is a check box named AutoUpdate. If this box is selected, then any change to the style will apply to all paragraphs using that style. (See Writer Manual Using AutoUpdate)
Use with care if you are in the habit of manually overriding styles in

My answer seems to have disappeared twice! Apologies if it there three times or if I have left two blank messages.

In the organizer page of the Paragraph Style dialogue box is a check box named AutoUpdate. If this box is selected, then any change to the style will apply to all paragraphs using that style. (See Writer Manual Using AutoUpdate)
Use with care if you are in the habit of manually overriding styles in your document!

Hi @petermau, Sorry – looks like you don’t get a warning when moderation is enabled!

No problem, glad there was a simple explanation for my multiple attempts.

Yes, the manual states: AutoUpdate - Updates the style when you apply direct formatting to a paragraph using this style in your document. The formatting of all paragraphs using this style is automatically updated.
Here is how this works: You have a style with AutoUpdate applied to your document. If you change the document format, the style is changed. This then changes everywhere in the document that style is applied.
This is not what I was after. I have a document where all the paragraphs have the default style. I would like to apply a style to the first paragraph of the document and have the Next Style applied, propagating or cascading through the document. If the styles are set as follows:
Heading 1 Next Style Heading 2
Heading 2 Next Style Text Body
Text Body Next Style Text Body
If Heading 1 is applied to the first paragraph, Heading 2 should be applied to the second paragraph, and the remaining paragraphs to Text Body.
Maybe this would create big problems now that I think of it. Such a pain setting every style of a large document though.