The search for a "Steam Master Server Updater download" usually refers to a legacy tool or fix intended for older games—particularly those built on the GoldSrc or Source engines (like Half-Life or Counter-Strike 1.6 )—to help them find servers after Valve's master server addresses changed. The Role of the Steam Master Server Updater
If you are looking for the current official tool, you do not want the Master Server Updater; you want SteamCMD. steam master server updater download
Steam Master Server Updater: Functionality, Security, and Distribution The search for a "Steam Master Server Updater