Kimchi Leader App Usage Experience and Curiosity

Before having a child, I used to enjoy reading books in Korean and relaxing at cafes. Then I found out about an app called 'Kimchi Reader' and decided to download it. When I opened the app, I could choose between learning methods such as YouTube/Netflix or short stories. I chose the latter and selected the last option titled 'Boat story including various grammar'. While reading, I marked only a few words that I didn't know, and checked the rest as words I knew, but this process was a bit tedious. So I tried to delete the words I knew and only keep the ones I wanted to use frequently, but it turns out you can only hide them, not delete. It's inconvenient that words like '있습니다' have to stay on the list forever. Does anyone know about this feature? I'm not very tech-savvy, so I would appreciate some help. 🤣