So I left Kimchi Hostel and went to take the subway train to Itaewon. I couldn't find the shop in the first round of walking around with the limited instruction that was posted in the forum and I can't remember the shop name as well. I took a rest in Starbucks then walked back towards the station on the other side of the road. I was about to give up hope when I finally saw the sign!! So I went up and I found the shop.
New World Plaza
2F Itaewon-dong 119-26
Yongsan-gu, Seoul
Subway: Itaewon Station, Exit 1.
Walk in the direction AWAY from Hamilton Shopping Center
The shop is not fanciful but it serves its purpose which was to provide clothes for plus-sized women. I asked if she had leggings (which was my goal) and when she said yes, I was so relieved. She found the leggings, and I tried them on and it fits!! So I bought 2 of those and walked around a bit more. I didn't see anything I fancy at the moment but I wasn't really looking for anything to buy at the moment.
At least now I know if I were looking for something to wear, I know where to look for it!