Trump should absolutely bring this up at the first sign of her bias Thursday night.
He should ignore Joe Biden because he's senile. Focus on the moderators and that they represent "fake news".
Point out that Fox News were not invited to host one of the debates.
The best way to do it is to somehow direct it to Biden. Trump, while answering something else, should say, "... and on a related topic, Ms. Bash, ask Mr. Biden what he thinks about your husband being one of the ones to sign off on the Russian disinformation hoax hiding all of the Biden family bribery and other corruption".