Chuseok is a Korean festival that celebrates the harvest and is also known as Korean Thanksgiving. If you want to greet someone during Chuseok, you can say the following phrases in Korean:

• 즐거운 한가위 보내세요 (Jeulgeoun hangawi bonaeseyo) - I hope you have a Happy Thanksgiving.
• 추석 잘 보내세요 (Chuseok jal bonaeseyo) - Have a good Chuseok.
• 해피 추석 되세요 (Happy Chuseok!) .
• 즐겁고 풍성한 한가위 되세요 (Jeulgeopgo pungseonghan hangawi doeseyo) - Have a Happy and Prosperous Hangawi.
• 좋은일만 가득하세요 (Joeunilman gadeukaseyo) - I wish you all the best.
• 즐겁고 행복한 추석 보내시길 바랍니다 (Jeulgeopgo haengbokan chuseok bonaesigil) - I hope you have a happy Chuseok.

These greetings are a way to wish the other person to have a great time during the festival and make them feel blessed.