This is a jukugo word that uses the on'yomi readings of the kanji. You haven't learned this reading for 代 yet, so here's a mnemonic to help you:
A change calls for a tie (たい). If you're the new company president, or you're going in to work to start your shift, you'd better make sure you look the part, so get that tie nice and straight.
This is the first change of company president in sixteen years.
In many sports, such as rugby, there are rules for substitution.
He didn't show up for his shift, and he doesn't answer his phone when I call him.