iOS rollback is not supported I am afraid, and also this sounds more like a hardware issue to me
Try this
- Remove all screen protectors, films or cases from your device.
- Check the opening of the speaker to see if it's blocked or dirty. On iPhone only, make sure the receiver isn't blocked or dirty.
- If necessary, clean the speaker or receiver opening with a small, soft-bristled brush. Make sure the brush is clean and dry.
- Go to Settings > Sounds (or Settings > Sounds & Haptics) and drag the Ringer and Alerts slider back and forth a few times. If you can't hear any sound, or if your speaker button on the Ringer and Alerts slider is dimmed, your speaker may need to be serviced.
- If you can hear sound, try making a call with your iPhone and turn on speakerphone. On iPad or iPod touch, make a FaceTime call. If you still can't hear anything, or you hear static or crackling, then your network or reception could be the issue. Try calling again later or from a different location
. After following these steps, you might still need to contact Apple Support to discuss service options.
