The clean command is used to delete the generated book and any other build artifacts.

mdbook clean

The clean command can take a directory as an argument to use as the book's root instead of the current working directory.

mdbook clean path/to/book

The --dest-dir (-d) option allows you to override the book's output directory, which will be deleted by this command. If not specified it will default to the value of the build.build-dir key in book.toml, or to ./book relative to the book's root directory.

mdbook clean --dest-dir=path/to/book

path/to/book could be absolute or relative.