It's super easy to fix, but we need root.
Copy and paste from OPO forums:
First you need a rooted device.
If you could, edit using a file explorer such as ES Explorer with root access
Then, edit /system/etc/audio_platform_info.xml
<device name="SND_DEVICE_IN_HANDSET_MIC" acdb_id="40" />
<device name="SND_DEVICE_IN_HANDSET_MIC" acdb_id="4" />
1. Go to system/etc/mixer_paths.xml
2. Mount system as R/W
3. Open up mixer_paths.xml with Text Editor
4. Scroll close to the bottom of the text, your little scroll position indicator should be about an inch up from the bottom of your screen(no on screen buttons)
5. You will see <!-- Analog input devices --> and a bunch of text underneath.
6. I wasn't entirely sure which mic would make this work so I changed the <path name+"main-mic"> value from 84 to 100. (Play around with the value until you find a sweet spot.) IF YOU GET ENVIRONMENTAL MICROPHONE INTERFERENCE, TRY TURNING THE VALUES BACK DOWN A BIT.
7. Save the changed mixer_paths.xml and reboot your device for good measure