Blizzard Regions in Destiny 2
Blizzard regions are the player's selected environment through which they are accepting to play with other players. Players may only play with other players who have selected the same region, and cannot join the games or activities of players in other regions. The player's selected region will also limit who appears in-game in a player's Friends Lists and Clan Roster.
When players launch Destiny 2 from the Blizzard desktop application, they will have the option to select their region of play. If the player takes no action to change their region, it will match the default region of the player's Blizzard account.
Players who wish to change their Blizzard region may do so by closing the Destiny 2 application, visiting the Destiny 2 landing page in the Blizzard desktop application, and selecting their desired region from the drop down above "Play".
For more information on Blizzard regions, please see this Blizzard article on Global Play: https://battle.net/support/article/7558