An editor in this case is a plain text editor, as opposed to LibreOffice Writer / MS Word which is a document editor. Examples would be Notepad, Notepad++, gEdit and Emacs. Googling “xml editor” would have added to that some editors with features like xml-highlightning (coloring the xml syntax, leaving the data intact).
Now, if you’re on Windows, please don’t use Notepad; it has a history of inserting wrong type of line endings (carriage returns). Notepad++ is a frequent choice on Windows.
To find the error you’d refer to the error message:
Read-Error. Format error discovered in
the file in sub-document content.xml
at 2,34352(row,col). What to do??
Someone explain simply? STILL NEEDS
This indicates row number 2 and column number 34352. Use the search feature from menu or Ctrl+F (most applications) to locate the placement in the file. Study the surrounding XML-entities (entries); are they different from the rest?
But if you read the linked question above, you see that the real reason in that case was a duplicate attribute at the beginning of the file. Check for such anomalies by opening content.xml in a browser (Firefox, Cromium, Opera etc), these will complain and highlight the error. Find that in your text editor, correct, save file and proceed to reintegrating content.xml into the .zip file you just created. Then rename it to .ods and test in LO.
Hope this helps.