change the subject
Deliberately talk about another topic, as in If someone asks you an embarrassing question, just change the subject. This term uses subject in the sense of “a topic of conversation,” a usage dating from the late 1500s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.