안녕하세요! I don’t know the whole sentence of this expression, but I hope it helps. 담다 is basic form of 담아. It means 1)put sth in sth. EX: put food on a plate. 2)keep or hold an idea or content. EX; You have to hold it in your mind. I believe that the “담아놨던” of the word is second meaing. 놓다 is basic form of 놨. ”놓다’ means sth lay, put place. It is same meam “두다”. “놨” is a shortened pronuciation of “놓았”(past tense 놓았다). What is the next “던”? A method of expression to indicate that the speaker has seen, experienced, recalled, and reported actions. EX: 내가 자주 갔던 식당입니다. 내가 좋아했던 노래입니다. Perhaps I imagine this whole sentence like this. ( 내가 오래 전부터 마음 속에 담아 놨던 말인데?= That’s what I’ve been saying for a long time.)