You can download the Ubnt Discovery Tool version 2.5.1 from the Ubiquiti website:
Ubiquiti has transitioned away from the 2.5.1 Discovery Tool. For better compatibility with modern hardware, consider these options: ubnt discovery 251 download link
The UBNT Discovery Tool is a software application designed to detect and identify Ubiquiti devices on a network. The tool allows administrators to easily discover, configure, and manage Ubiquiti devices, including access points, routers, switches, and other network equipment. With the UBNT Discovery Tool, you can quickly and easily identify devices on your network, view their current configuration, and perform firmware upgrades. You can download the Ubnt Discovery Tool version 2