To perform a hearing test, you need to use the EPOS Sennheiser ADAPT-360 headphones, they are provided as part of the TympaHealth kit.
Before beginning the hearing test, the headphones need to be powered on and connected to the TympaHealth Android device via Bluetooth, having the volume turned all the way up to the maximum.
Typically, you simply need to power on the headphones and they will automatically connect to the mobile device - you can then start the hearing test. In exceptional situations, for example when you received replacement headphones, you will have pair them with the mobile device. Here's a video explaining how to do the Bluetooth pairing:
You can find additional information about the headphones in their manual.