The US has done no investigations related to this claim. According to Blinken:

“We haven’t had the ability to investigate [the allegations] ourselves. But they are highly, highly credible,” Blinken said during a press conference.

Source: https://www.timesofisrael.com/blinken-says-evidence-of-unrwa-staffers-oct-7-involvement-highly-highly-credible/