To compensate for the empty spot, I joined the bowling game.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means supplement so the verb vocab version is to supplement.
Oh, gee, now (おぎな) you're going to supplement it? That would have been helpful earlier. Might help to say "oh gee now" with a ぎ sound instead of "ji" sound out loud, too. This is a tricky reading, won't be learned too easily, so think about it a bit now.