It is scheduled to be released in the US on July 5, 2019, by Lionsgate, and in the United Kingdom on May 17, 2019 by Signature Entertainment.
Currently (January 13, 2021) available via STARZ subscription, for example at Amazon Prime with STARZ.
Updated 1st April 2021: this is currently on Netflix (at least in the UK it is)
Update, 13 April 2022: available for rent or purchase on Amazon, Apple TV, Google Play, YouTube, Vudu, Microsoft Store, Redbox, and DirecTV. Also available on the Roku platform to stream.