How to cite a chapter from a report with different authors?

If authors are identified for the chapters, then this document is best treated as an edited collection. In this case, the chapter authors are the author and the chapter title the title. The overall report title is then the collection title (filling a similar role to journal title) and the "main" authors the editors.

The exact details of how this is formatted depend on the style where you are submitting, but if any names are appearing in the main text, they are of the chapter authors.