With Wind°ws and Odin3 and the latest stockROm firmware Android Oreo 8.0.0 including March 2020 Security Update this is done in a few minutes. The “hero2lte” is after the operating system change as in the original state.
download the latest firmware for your phone here. Select the precise model and your country. Click on the latest version, and on “Free download” or something like that. You just need a dump account. It will take 1h or 1h30 to download.
Then open Odin, plug your phone in download mode (power + home + volume down). Click on “AP” and select the downloaded file (maybe it needs to be unziped). Click on start once it’s ready.
The phone will reboot on the stock ROM (if you leave “auto-reboot” checked).
In download mode, You can only start flash processus one time with Odin,
then you have to reboot the device in download mode to start another flash processus
Did you finally succeed in reinstalling your Galaxy S7? I have the same thing to do on my own S7 and I would be grateful if you could share how you did it for yours.