Download STM32CubeIDE from https://www.st.com/en/development-tools/stm32cubeide.html and install it (the IDE is also required by Robot firmware).
Open the IDE by, for example, searching "STM32CubeIDE".
Import the project for Drone firmware by File -> Open projects from file system and select this directory as the import source.
Compile the firmware by Project -> Build Project and you will find the binary at Debug/Drone.elf.