https://www.gamespot.com/articles/new-pubg-savage-map-how-to-get-beta-access/1100-6457847/

PlayerUnknown's Battlegrounds' new map, Codename: Savage, officially enters player testing on PC tonight. The game's closed experimental server goes live at 7 PM PT / 10 PM ET ET (3 AM BST on Tuesday), and players can now sign up to give it a try. The test runs from now until April 5 at 4 AM PT / 7 AM ET / 12 PM BST.

You can sign up to access Codename: Savage's test server here. PUBG Corp. says this is a smaller test, and you'll need a copy of the base game already to play. The developer also says it plans to run bigger tests in the future, once it's "gotten the map into a better state."