Data issues

So I recently got a new iPhone in September. We have a limited amount of GB we can use each month. The problem is according to the Phone usage the thing that is taking up the most storage is the SYSTEM!! With just over 8 GB it even beats the amount I’ve used with Cellular Data by a mile, and I’ve only used 5 GB with that, and that’s followed by an app at 1.6 GB. How can I free up space from the system?

Side question, what exactly does “Reset Statistics” in Cellular Data do?