For some reason, it doesn't work for me. But I was able to find my representative here: https://www.house.gov/representatives/find-your-representative
That's great, but I should note that that tool is for the House of Representatives, and your OP is about the bill in the Senate. But that's okay because you should also contact your representatives about the House equivalent bill, HR 987, and you should mention that bill in your OP as well as S 401!
As for the original tool, sometimes you have to refresh the results page before it works.