The window that you see is to calibrate the microphone, you have to press "Start" and blows toward your device microphone. You should see the bar on the right became green.
After three blows the window should close itself, if it does not happens continue blowing.
If you cancel the calibration, you will be prompted to do it the next time you open the App. To avoid to be prompted, you can disable the microphone: open the slider on the left, click the microphone button and set the volume to zero.
You will be still able to blow bubbles with the "blow" button on the bottom right of the screen.