How to get there...
1. Take Line 5 (Purple Line) to Mokdong Station
2. Exit the station via exit 8.
3. When you exit you will see a Daiso on your left.
4. Walk straight ahead for about 2 and a half minutes. (You should be on the left side of the road). When you reach the Paris Baguette, turn left.
5. Walk for 4 minutes, you will pass a play park on your left. After that you will see a wall with scenes from the Giving Tree on your right. Keep walking straight.
6. After the giving tree wall ends, walk for 2 more intersections. You will see the SDA Language Institute building on your right.
7. Welcome to Mokdong SDALI, the church is on the 5th floor.
Finally, here is the address in both Korean and English.
삼육어학원 서울시 양천구 목동로 9길 23
#23, Mokdong-ro 9-gil, Yangcheon-gu, Seoul, Korea
And here it is on Google Maps.