My dataset has not a channel file , maybe the channel locations existing into data file recording or not ?
Knowing that my dataset existing in this link : EEG Motor Movement/Imagery Dataset v1.0.0
Knowing that my dataset existing in this link : EEG Motor Movement/Imagery Dataset v1.0.0
If you want to do some source estimation, you need 3D positions.
Right-click on the the channel file > Add EEG positions > ...