How do I reference a work with no author of which a new edition has been published?

If no author or organisation is listed, start the reference entry with the title. In case of a second or subsequent edition, the edition is mentioned directly after the title and before the year.

Merriam-Webster's collegiate dictionary (11th edition). (2019). Merriam-Webster.

Parenthetical citation: (Merriam-Webster's collegiate dictionary, 2019)
Narrative citation: Merriam-Webster's collegiate dictionary (2019)