I don't have a WaveEngine (yet) myself, but I do have the IceCap Dual Pump Controller which uses the same HYDROS app.
I am able to change the name by switching the HYDROS connection from WiFi/Cloud to Bluetooth, clicking those 3 dots in the upper right-hand corner, and clicking "rename device."
If that doesn't work for ya, I'd suggest emailing our support staff so they can lend a hand. You'll probably receive a reply later today!