How to best root my former AT&T (now unlocked and running on Cricket) S6?

Model #: SAMSUNG-SM-G920A
Build #: LRX22G.G920AOF4

I bought this phone used off amazon. It's still got AT&T branding, but it's unlocked and I'm running it on a Cricket SIM. Just wanna root it. Don't care if it breaks KNOX since it's not covered anyways. Still on 5.0.2 :(

Thanks!

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