The long and short of it is that Triggertrap Mobile does not have a Bluetooth function.
We did try to include an experimental implementation of a Bluetooth feature, but we never were able to get it to work reliably. In the end, we concluded that our particular implementation of Bluetooth was not a reliable enough signal to consistently trigger your camera. On top of that, it tends to be a lot slower than a direct connection or even Wi-Fi.
We may try and bring back Bluetooth to Triggertrap Mobile in the future, but currently Bluetooth is not supported as a part of our app.