You can add missing seasons and episodes yourself (if you have some reliable source - the best is official website of the series). Just change temporarily TV series status from "Ended" to "Returning series" and you will be able to add new seasons.

시즌 추가가 안된다.. 시즌 추가를 할려면 자격이 필요합니까? 현제 포테마요 시즌 추가 및 변경이 안됩니다.

You can only add new season when you change the TV series status from "Ended" to "Returning series":

방영 종료 ---> 다음 시즌 방영 예정

I've already changed it, so please just set it back to Ended / 방영 종료 when you're finnished with adding new seasons.

Thanks