Due to the rain on Saturday, the Sports festival was postponed and changed, so today became the compensation day-off.
ご質問ありがとうございます。
この場合、「土曜の運動会が雨天順延になったので今日は[代休](https://eikaiwa.dmm.com/uknow/questions/13542/)」と言いたいなら、英語で「Due to the rain on Saturday, the Sports festival was postponed to Sunday, so today happens to be the compensation day-off.」と言えます。
ご参考になれば幸いです。