The update, titled "The New Era Begins," was actually released on December 15, 2022 . While you are looking for a "2021" trainer for version 1.58, that specific version did not exist in 2021; the active versions during 2021 were 1.56.x and 1.57.x .
Update 1.58 - The New Era Begins! · Battle Realms - SteamDB battle realms zen edition trainer 158 2021