tone down
tone down {v.}
To make softer or quieter; make less harsh or strong; moderate.
He toned down the sound of the TV.
She wanted the bright colors in her house toned down.
When the ladies arrived, he toned down his language.
The strikers were asked to tone down their demands for higher pay so that there might be a quicker agreement and an end to the strike.
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Source: A Dictionary of American Idioms