Glad you asked @id1 ! If the above instructions did not work, please try tapping on your Chime/ Chime Pro in the app > tap Alert Settings > tap Chime Tones > here you should see that volume slider. Please let us know if this worked for you 
Glad you asked @id1 ! If the above instructions did not work, please try tapping on your Chime/ Chime Pro in the app > tap Alert Settings > tap Chime Tones > here you should see that volume slider. Please let us know if this worked for you