Hi there Annette264,
If a certain app on your Apple Watch has lower than expected volume, let's first restart your Apple Watch. This refreshes the software of the device and resolve unexpected behavior like this. This shows how: Restart your Apple Watch
" How to restart your Apple Watch if you have watchOS 9
- If your Apple Watch is charging, take it off the charger.
- Press and hold the side button until you see the power button
in the upper-right corner of the display. - Tap the power button.
- Drag the Power Off slider.
After your watch turns off, press and hold the side button again until you see the Apple logo.
How to restart your Apple Watch if you have watchOS 8 or earlier
- If your Apple Watch is charging, take it off the charger.
- Press and hold the side button until you see the Power Off slider.
- Drag the Power Off slider.
- After your watch turns off, press and hold the side button again until you see the Apple logo."
If this continues after restarting, try adjusting your audio settings using the steps in the 'How to turn your Apple Watch volume up or down' section here: Change the audio and notification settings on your Apple Watch - Apple Support
If you need further assistance, our Health and Activity Support would be the best equipped to investigate what's happening. They can be reached under Apple Watch > Health & Fitness here: Apple Support
Take care!