The value of trade in for iPad Pro 3

Hi, I got an iPad Pro for 12’9 inch, WiFi+cellura, 256 G, Space Grey, and I just trade in my used iPad and paid $599 and got this new iPad Pro 12.9 inch, and all the things is new I never used it, the original screen protector still on it, also have the charging power, however, if I don’t want this size and I want IPad Pro for 9 inch, can I trade in again? Or I just go to store change to 9 inch’s iPad?