There is no audio device selection on iPad, and both my monitor and AS315 have speakers, how to make sure to output sound by AS315, instead of the monitor?

iPad’s design outputs sound to the audio device that gets connected last. Refer to the following steps to get audio output from AS315.
 
1. Connect the monitor to AS315’s HDMI port.
2. Take the pigtail USB Type-C cable of AS315 and connect it to iPad.
3. If the power supply needs to be charged, plug it into AS315 after the steps above.