I'll give you some info to put you in the right direction.
So basically what happened is that the phone had a custom binary flashed on it which is at the very least a custom Recovery or Root file.
Now since the phone is displaying Custom Binary Blocked by FRP lock there is no way around it without reflashing latest original stock Samsung Firmware and doing a factory reset on the phone.
If you want to keep data you'll need to take the phone to a reputable phone repair shop that utilises GSM box (flash / unlocking) boxes as they can unbrick the phone without resetting it.
For the flashing part make sure firmware being downloaded is the latest one. Always check via Sammobile with model no of phone e.g SM-G935F. And the CSC which is a 3 letter sales region code that is displayed usually on the download mode screen as Carrier_ID.
To get into download mode you simply hold power, vol down and home until you get the light blue screen with text prompt. Follow instructions to enter download mode.
Make sure to use latest Odin so that latest OS firmware is compatible with flashing program.
Sammobile has download (DL) link for Odin when firmware is selected to prepare download.
Best way to DL firmware is to use the SamFirm application from XDA Developers forum thread, when you google search that app you'll find it.
If you get SW Rev check fail Bin:x SW: X it means firmware flashed is too much older than the current firmware on the phone. To fix that simply flash newer firmware. You'll need to re-enter download mode to flash again.