How is the universe still expanding if the seven heavens have already been made?

It is known that the earth and heavens have already been made in 6 days. The lowest heaven is our observable universe. In Quran 51:47, it is written “We built the universe with ˹great˺ might, and We are certainly expanding ˹it˺.” So my question is that if the heavens and earth have already been made, how is it that it’s still expanding. Same with earth, as it’s already been made how is it still undergoing changes today? Jazakallah Khair