Still learning how to use this, but after a recovery save when laptop died, it came back with this weird blue box in my header that I can’t delete? Any ideas how to fix?
thanks in advance 
A screenshot is of no use in such a case. Attach the offending file. Don’t forget to mention OS name, LO version and save format.
I have uploaded a copy here since I can’t attach the file directly.
Running on macbook and saved as .odt file
Version Info:
Version: 24.2.5.2 (X86_64) / LibreOffice Community
Build ID: bffef4ea93e59bebbeaf7f431bb02b1a39ee8a59
CPU threads: 4; OS: macOS 13.6.9; UI render: Skia/Metal; VCL: osx
Locale: en-NZ (en_NZ.UTF-8); UI: en-US
Calc: threaded
sorry, as I said, only just learning to use this system and really hoping I don’t have to start all over to fix it lol. thanks
The header of page style “chapter 2” has some background image set. Remove it, save and reload the file.
I would redo the entire formatting of that document by means of styles. This is a typical MS Word document, chaotic beyond repair.
Your document was initially written as DOCX. At some point you switched from Word to LO Writer and it underwent several (many?) edit sessions before converting to ODF. This is evidenced by the many spurious character and page styles created by the conversions from DOCX to ODF and back.
Your document is now saved as .odt (native ODF format) but its structure, notably the pages, is already damaged beyond repair.
This is even made worse by your usage as a mechanical typewriter. Though you applied a few styles, most of your text is direct formatted with wrong styles in your empty paragraphs (for vertical spacing) which are responsible for TOC pollution and other side effects.
Your worst mistake is your use of Default Paragraph Style in your narrative.
The blue box
I could not get rid of it. I think this is a consequence of the catastrophic effects of handling a non-native format document through numerous edit sessions.
The probable cause is the difference in the page model between Word and Writer. In Word, margins are external to text area and serve as a container for various data like header or footer. In Writer, margins are no-print area. All contents is taken from the “text area”: header, narrative and footer.
In principle, this difference is taken into account when converting, provided the contents is rather correctly structured. This does not seem the case here with your image.
Your image is anchored to the header (good) but you requested positioning relative to the page (top and center) making it ipso facto (or logically) independent from the header. And your header no longer adjusts automatically to the image size.
IMHO this blue rectangle is a spurious fossil of the multiple format conversions before you switched to .odf.
And your document is damaged in weird aspects: I tried to see if you had some background or highlighting in your header. I went to the Area tab of the page style. It reports None. But when I look at the (contextual menu) header Border & Background, now there supposes to be an image. The selection does not make sense and changing it has also no effect.
Fix
The only solution is to recreate your document from scratch. Paste its whole contents as Unformatted text into a blank document and apply consistently styles (paragraph, character and page), removing absolutely all direct formatting including your empty paragraphs for vertical spacing.
This probably requires you read the Writer Guide and you practice styling on scratch documents. Note that styling will dramatically reduce your document size compared to direct formatting and offer you ease and comfort when it comes to layout and formatting tuning.
Suggestions
With correctly designed paragraph styles, in particular those for Heading n, you need no change in margins for the first page of your chapters. Just customise Spacing above and perhaps add an automatic page break.
If your image is some sort of cul-de-lampe to flag chapter start, anchor it to the Heading 1 chapter heading paragraph. Define a frame style for it with adequate parameters (relative to paragraph text area will be easiest and more logically connected to the paragraph; wrap None is also suggested). And you can also create an AutoText entry to start your Heading 1 with the image attached so that you no longer have any manual operation at start of chapter.
As @ajlittoz has said, the document has an unnecessary number of styles coming from a conversion from another format, I think with another software, for example. OCR. with a chaotic structure.
I have managed to remove the blue stripe that is in the header of the Chapter2 page style.
- Copy the image inserted in the header to another part of the document so as not to lose that image.
- Remove the header from the page style (which removes all content from the header including rare formats that are difficult to detect)
- Add a header to the page style again
- insert the image in the new header.
- Even so, for the document format to be stable, it is necessary to follow the recommendations of @ajlittoz