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 to learn the もち portion of もちいる:
What will you utilize to get the job done? You have mochi (もち) in your hand, so you'll use that. Now go think of some kind of imaginary task you'll complete with mochi, making it as ridiculous as possible.
There is a person who uses a name similar to Tofugu.
North Korea uses nuclear weapons to threaten others.
I tickled her with a brush used for painting.