Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
When you only have one thing, there's only one thing. Nothing is collected. But when you have two... "ah two!" (あつ). Now you're starting to collect something.
Please gather the people wearing blue shirts.
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I am collecting pictures of foreign food.