Looking for UK Three Network 4G Super-Voice enabled firmware

I currently own the Galaxy S7 edge UK (unlocked) unbranded handset, however my network is with Three. Supposedly you need to have bought the handset from them to have 4G Super-Voice (VoLTE/HD-Voice) enabled, so I'm wondering if anyone can help me source the firmware. I'm sure this will be useful to anyone else on the Three network with an unbranded handset.

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