https://www.pcgamer.com/pubg-sanhok-map-returns-to-test-servers-this-week/

PlayerUnknown's Battlegrounds' Sanhok map returns to its 'Experimental Server' this week. Once known as Codename Savage, the tropical 4x4km arena enters test servers on May 31 at 7pm PST/ June 1 at 3am BST, and wraps up on June 4 at 4am PST/ 12 noon BST. 

"As before, everyone who owns a copy of PUBG will be able to play simply by downloading the updated version of the 'PUBG: Experimental Server' found in your Steam library," explains this Steam Community update post. Developer PUBG Corp notes that this phase of testing will likely be the map's last. All going to plan, this means Sanhok will hit live servers "near the end of June".