swallow (one's) words
To retract or rescind something one has said. He'll be swallowing his words once I show him the sales figures for this quarter. I knew I had to swallow my words when she beat me in that game of chess.
swallow one's words
Take back what one said, as in If they win I'll have to swallow my words. George Farquhar used this idiom in The Inconstant (1702): "I have swallowed my words already; I have eaten them up." For a synonym, see eat one's words.