To fix this issue, please try the steps below:

1. Remove the maximum volume limit on your phone. Go to Settings > Sounds & Haptics > Headphone Safety and turn off Reduce Loud Sounds.

2. Make sure the charging case has enough power and reset the earbuds as per the steps below:

- Place the earbuds in the charging case and leave the case open. 

- Press and hold the charging case button for 10 seconds until the LED strip flashes white rapidly three times. This confirms that the reset is successful. 

3. Re-pair your earbuds and turn up the volume of both your phone and earbuds with the music/video to the maximum.

4. Use a Q-tip with a bit of rubbing alcohol to gently clean the metal mesh filter under the rubber ear tips.