Because LASR X is a web app, there are no special sound settings in the app. You'll need to check a few things on your iOS device to get sound working.

First, if your phone or tablet has a hardware "Do Not Disturb" button on the side, make sure it is flipped off (so the red dot is not showing).

Second, make sure the volume on your device is turned up. You can use the hardware volume buttons on the side (if your device has them) to turn up the volume.

Lastly, swipe down from the battery indicator at the top-right of the screen. Adjust the volume as needed and be sure the "Do Not Disturb" feature is turned off: