Idiom/expression for changing the subject in a conversation

"Moving on!" is an idiomatic phrase used (at least here in the US) when a topic gets too touchy or if the conversation bogs down on a particular aspect of the subject and the wish is to keep it moving past that point.

Let's move on to the price of eggs...

Not actually the price of eggs or anything related to it. Just a sarcastic phrase used in a conversation when one tends to gloat off the subject.

Urban Dictionary

This seems to coopt the sarcastic 20th century rejoinder, What's that got to do with the -- ?:

an idiom denoting an irrelevance or non sequitur in the current discussion.

A common form "what does that have to do with the price of tea in China?", is a retort to an irrelevant suggestion. This facetious usage implies that the topic under discussion might as well be the price of tea in China for all the relevance the speaker's suggestion bears on it...

• In the United States, the phrase "What's that got to do with the price of eggs?"...
• The British equivalent is "What's that got to do with the price of fish?" or "What's that got to do with the price of meat?"
• A Scottish variation is "What's that got to do with the price of cheese?"...
• and a Northern Irish variation is "What's that got to do with the price of a sausage?"

Wikipedia.org

The specific item can be altered for maximum comic or sarcastic effect.