Chapter headers are usually obvious as 'Chapter 1' or Titles at the top of a page with text beneath. Check the Table of Contents if in doubt. This is often linked to on the Project Page, otherwise find the contents page by clicking on Images, Pages Proofread & Differences on the Project page. The page you are looking for will probably been among the first ten .png images in the first column. Project managers(PMs) will sometimes specify exceptions in the Project Comments.
The Formatting Guidelines state:
Format chapter headings as they appear in the image. A chapter heading may start a bit farther down the page than the page header and won't have a page number on the same line. Chapter Headings are often printed all caps; if so, keep them as all caps. Mark any italics or mixed case small caps that appear in the image.
Put 4 blank lines before the "CHAPTER XXX". Include these blank lines even if the chapter starts on a new page; there are no 'pages' in an e-book, so the blank lines are needed. Then separate with a blank line each additional part of the chapter heading, such as a chapter description, opening quote, etc., and finally leave two blank lines before the start of the text of the chapter.
Old books often printed the first word or two of every chapter in all caps or small caps; change these to upper and lower case (first letter only capitalized).
While chapter headings may appear to be bold or spaced out, these are usually the result of font or font size changes and should not be marked. The extra blank lines separate the heading, so do not mark the font change as well. See the first example below.