How do I change format from “music” to “audiobook” if dropdown menu doesn’t give “audiobook” option?

When I purchase audiobooks from other companies, I import into iTunes. Import defaults to music — I have to change format to audiobook. Sometimes this is not an option, and I don’t see audiobook as part of the dropdown menu. Is there another way for me to change the format? If the format is music, then the audiobook doesn’t show in my audiobooks, but shows as music. Help!