This what can be done with App Inventor to control the Speech Recognizer
The" I do not understand" is a new feature introduced by Google to improve performance. Unfortunately, when that icon displays, App Inventor cannot capture it. Sorry, this once upon a time worked when the recognizer did not recognize; the example no longer works for that instance. There is no way to get past it other than touching the icon. You cannot do everything with the Speech Recognizer professional developers do with Android Studio while using App Inventor 2 .
The pop up can be hidden if you program your app using Java and Android Studio or to develop a Speech Recognizer extension for AI2 that would hide the pop up. I am not aware of any extension that can help. Someone else might comment.
Your options are to code your app using the Java based free Android Studio. It can handle the Speech Recognizer much, much better than App Inventor can.
Do you have a sense of humor? Get a very long stylus and poke your screen (which might work). or a short stylus attached to a yard stick. Sorry, you are not going to be able to make the SpeechRecognizer work as you would like unless MIT eventually includes a block to recognize when the 'I do not understand' is evoked.
One possible solution is to always speak in a loud clear voice. My tablet, that has a very good cpu, recognizes about 95% of what I say to it. It is very friendly. However, my phone is a jerk. It only understands me about 60 to 70% of the time. Both devices have difficulty understanding my wife (really); she thinks it is because the recognizer is a lot like me.
The speech recognizer is very fussy, so your only defense is to talk clearly, with an even cadence in short sentences or phrases.
Regards,
Steve