When you connect an activated iOS device in Blancco Mobile Diagnostics and Erasure, the device will be shown in 'Requires attention' status in Blancco Mobile Diagnostics and Erasure. There is also query on device screen asking to verify that you trust the computer.
Accepting the query is only required if you're running diagnostics for the device. With some devices it is also required to re-connect device after this to get the device to 'Connected' status.
Accepting the query is not required if you're erasing the device. You can simply start erasure without accepting the trust query on the device.