I am Vinod. I will try my best to help you resolve this issue.
Unfortunately, we can't turn on the sound. But icloud may be able to ring the song for you. Have you tried through icloud (find my iphone) playing the sound? If not, go to the following website
Once you sign in, click on "all devices"at the top and
Click All Devices, then select the device on which you want to play a sound.
In the device’s Info window, click Play Sound.
If that does not work, I would suggest you to try ringing the phone at night after turning off all the lights.
Hope this helps. Let me know if you find any difficulty