3D Scan Help

So I’m new to 3D scanning, I’ve been 3D printing for a few years and have just recently gotten into using freecad and I just got a Creality Otter scanner and have learned how to scan something and get it to my 3D printer, my question is how do I go about scanning an object and then making a “part” to fit what I scanned? Example : if I wanted to make a phone case and had a scan of the phone, what is the best way to go about taking the scan of the phone to design the case? Any help with this would be greatly appreciated!