Install AudioBookConverter from Steam. Using Steam will guarantee you are using safe, latest and genuine version of product.

Launch AudiobookConverter. By default you will see Queue tab where conversion jobs will be displayed. Application is ready for conversion.

Use add button to add ether directory containing source files or source file. Depending on your book size and on your drive speed this may take several seconds to display all files.

Important note: at this moment application starts to scan source file to load meta-information: tags, codecs, duration, bitrate, etc. to prepare you for next steps. So, if you system is not very powerful and you added quite a lot files you may see system is not very responsive.

When AudiobookConverter loads tags from source files it will populate fields at the bottom of the screen. Now it's time to input correct audiobook information or keep it as it. Note: correct book information is important when importing to iTunes or Books application as they heavily relay on tags.

You can right-click on the file and move it up or down or even remove it if you don't need it.

Press Chapter button and application will parse existing chapters in m4b. If you happy with default chapters split you may move one.

You still can manage chapter move/remove/combine/split/edit them before converting.

It is important to select Split by Chapter, so each chapter from m4b book will be used to create separate mp3 file.

Each chapter will be converted as a separate job, so you will see many chapters converted simultaneously into output folder you select.