Does anyone know how to adjust the brightness of an Adafruit Featherwing Charlieplex 15x7 LED Matrix?

I'm using the Wire.h, Adafruit_GFX.h, and Adafruit_IS31FL3731.h libraries and the function I want to dim is below:

```
matrix.setTextSize(1);
matrix.setTextWrap(false);
for(int8_t x=0; x>=-32; x--) {
matrix.clear();
matrix.setCursor(x, 0);
matrix.print("Jeepers!");
delay(150);
}
```

I've tried to use matrix.setBrightness() and this function isn't available in those libraries for some reason, and I've also tried adding to the end of the string the brightness with no success.

Other functions using bitmaps can adjust the brightness accordingly at the end of a string, but there doesn't seem to be an available function like matrix.setBrightness() that I would need.

Thank you for your help and consideration.