After the LORD answered David with fire from heaven, what did the angel do with his sword?

Answer: Put it back in its sheath

The LORD spoke to the angel, who put his sword back into its sheath. Seeing that the LORD had answered him, David offered sacrifices there.

“Then the LORD spoke to the angel, who put his sword back into its sheath. At that time, when David saw that the LORD had answered him at the threshing floor of Ornan the Jebusite, he offered sacrifices there.”— 1 Chronicles 21:27-28 (BSB)