This has to be disappointing to Fox News. It seems that Hillary Clinton did get a small bounce after the first debate. Fox's own poll shows she won the debate (57% to 19%), and they now show her with a 4 point lead over Trump in a 4-way race. As the chart below shows, Clinton's favorability rating is higher than Trump's also, and has been since June.
The Fox News Poll was done between September 27th and 29th of a random national sample of 1,009 registered voters, and has a margin of error of 3 points.