Bluetooth error with App Android

[epyc]

Hi,
Trying to code and play with my boy i got this error with your bluetooth app :

- the Android BlueTooth control app does not find the receiver. When I push the 'Start' button, it says 'Please select Blue/Yellow channel, but I do not understand how/where to do that.
I see a message talking about pressing a select button for 3 seconds but i don't know where is this button...

Thanks