Well of course you can apply a gain to the signal.
There are a number of ways to do this.
The simplest way would be to use an alsa mixer control, IF there is one available for the dmic, which I don’t know. Look for things labeled volume or gain that seem to be tied to capture and/or dmic. Note that digital microphones don’t technically have a volume control on them, which means that if this mixer is implemented, then what it is doing is applying a digital gain to the signal.
The next option would be to use an alsa filter. First of all, I notice from the instructions you linked to that you are running debian, which means that you will have access to a full blown alsa rather than the tinyalsa in Android. That means that you can add filters. Near the bottom of this link they talk about adding a volume control for a digital microphone, obviously you would have to adjust for the differences between rpi and db410c, but the same approach is applicable; https://learn.adafruit.com/adafruit-i2s-mems-microphone-breakout/raspberry-pi-wiring-and-test
And the third option will be to manually apply a digital gain to a captured audio stream. There are a million tools you can use to do this, like ffmpeg, or audacity.