https://www.gamespot.com/articles/last-chance-septembers-free-legendary-pokemon-avai/1100-6461365/

A new month is now upon us, and The Pokemon Company is continuing its Year of Legendary Pokemon campaign with another pair of free Legendaries for Ultra Sun and Ultra Moon. During September, players will be able to claim one of the two Eon Pokemon from Ruby and Sapphire, Latios and Latias, but as usual, the way to get your hands on them will vary by region. [Update: The Latios/Latias distribution is set to end today, September 29, making this your last opportunity to pick the Legendaries up.]

Once again, those who live in the US will need to go to a participating retailer to pick up a free download code for the Legendaries. This time, the code will be distributed at Best Buy stores around the country from September 2-29. Players in Europe and Australia, meanwhile, will be able to download the Legendaries directly from the Nintendo Network between September 1-23.