How to restore iPhone 5s 10.2 that someone else jailbroke, set up as new 10.2

Howdy y’all. Long time no talk. Currently rocking one of our loaner phones, a Kermit the Frog coloured iPhone 5c 32GB, non jailbroken, first time using a non jailbroken phone ever as a primary device. My highly customised 5s on 9.3.3 went for a swim, recovered it enough to get the data but won’t get signal and won’t sync, yes I tried a new dock connector.. Just picked up another 5s on 10.2 in mint condition though. This device unfortunately was already jailborken (sic) and tweaks installed by another user. I purchased it a JailbreakersUnite this past weekend in NYC. I was able to remove all data as far as I can tell except for cydia and the tweaks and customisation presumably already installed. How do I set this thing to as stock as possible so I may run my own jailbreak and/or restore from my own back up and over ride previous owners tweak settings. Ideally, I’d like to remove all their tweak settings, then rerun the jailbreak somehow. Currently Cydia does not open but I can see a blue Cydia icon on springboard and there are a bunch of tweak icons as well. I’m guessing it’s in the unsigned tethered mode or whatever. Would really appreciate a walk through on this one. Thanks in advance from a long time member who has been MIA for a while. 😉