This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means immersed, so the verb version is what happens when you immerse something in a liquid. It's to soak or to dip.

Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You already learned this reading when you learned 浸る, so you should know this one too.