To adjust the speaker volume of your camera, tap Settings above the camera's thumbnail.
Select Audio Settings and you will now see a slider to raise or lower the volume on the camera side. This will only control the camera's volume and not the audio level on your phone or tablet.
If you do not see this option in Camera Settings, fully close and then re-open the app. If you still don't see this option after doing that, feel free to contact support here and we will help troubleshoot with you.