How to edit switches\shortcut arrangement?
I believe you have restored an earlier backup when setting up your device. That's what caused the edit button to disappear. The edit button isn't generally backed up and when restoring it, it will be missing. There are a few methods to solve this :
Method #1 - Install SystemUI Tuner from PlayStore and reset the quick settings panel.
Method #2 - Using ADB (download platform tools to your PC) : Download