An ancient Chinese bird kept its feathers, and colors, for 130M years
washingtonpost.com
washingtonpost.com
Uranium lead dating is typically held as accurate for rocks between 1 million and 4.5 billion years ago, so they probably used this. However, there may not be any uranium in the fossil itself so they may have looked at stratigraphic layers of volcanic ash, which would have sufficient amounts of uranium, above or below the fossil to arrive at this date(1). This is really speculation without looking at the study where I'm sure they discuss it in detail.
(0) https://en.m.wikipedia.org/wiki/Radiocarbon_dating
(1) https://en.m.wikipedia.org/wiki/Uranium%E2%80%93lead_dating