Your MyTag has been designed with a balance between battery life, speaker size and alert volume. Sounding its alert is the biggest use of battery power, and repeated use of the alert can reduce battery life. Therefore we have had to balance alert volume with battery life.
While we cannot increase the volume, you can try different alert rings on the MyTags. We find some people have hearing that responds to one alert melody better than others, due to the frequencies in the alert.
On the App, if you choose the MyTag you want, then go to Settings (the little gear wheel), then scroll down to near the bottom, you will see the option to change the ring tone on the MyTags. Change the ring tone, then ring the Tag. Try each ring tone and see which is best for you. Make sure you change the Tag ring tone, not the phone alert ringtone.
If you are trying to find your MyTag and you can't hear it, there is a "Signal Strength" indicator on the app - move around the house and the signal strength reading will go up when you are closer. As you get closer you will then be better able to hear the Tag ringing.