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: In fact, while you're sitting there with no cares, waiting for things to become untied, you stare down at your toe (と). Really imagine doing that while things around you are getting untied.
Your shoelaces are untied. That's dangerous, you should hurry up and tie them.