Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
What'll you drink now? I'll have a Zima, ima.
Say "ZIMA IMA" ten times fast.
I’m reading the newspaper right now.
What was I doing until now?
Now I’m going to say good morning to my helmet.