Yes, you can turn off your own webcam. Click on the camera icon in the right panel. You can also turn off the tester's webcam, from an camera icon next to their name.
We do not recommend turning off your own webcam during the start of the interview. Test participants will generally feel more comfortable and will let them know there is a real live person in the session if you keep your camera on. This helps to build rapport with your customers and/or participants.