Despite being in the process of building a new pair of lightsabers, Ahsoka manages to fend off the Sixth Brother and eventually use the Force to take the Kyber crystals from his lightsaber. While this is happening, the humanoid frantically tries to deactivate his lightsaber’s spinning feature; however, the device quickly becomes unstable and explodes, killing him instantly.
Ahsoka later scrubs the crystals of all dark side energy and uses them to forge her new twin lightsabers.
Source: https://www.distractify.com/p/the-sixth-brother-tales-of-the-jedi