Check out
the documentation for CHRMAK, accessible from the docs section of the website. Better yet, if you don't like command line conversion tools with plantext config files use VOpenCHR instead, it's an actual editor. It's listed on the sidebar for reference. If you read my newer tutorial, it explains how to import sprites into VOpenCHR, editing them is fairly straightforward, and I believe you can figure it out if you have any experience with drawing programs whatsoever.