Some sources do not include page numbers, such as websites and some ebooks. You then need to use other ways to show the reader where you found the quoted text. Use the way that makes it easiest for the reader to understand!
If a heading is very long, you can abbreviate it.
Instead of a page number, provide a time stamp for the beginning of the quotation.
Read more about quotations of material without page numbers on APA Style: Direct Quotation of Material Without Page Numbers