I found some links dealing with similar issue
Internal microphone not working on Acer swift3 alc256 - Technical ...
Type in terminal:
sudo apt install pavucontrol
To restart machine type:
sudo systemctl reboot
If after restart there will be no sound, type in terminal:
sudo nano /etc/modprobe.d/alsa-base.conf
to the end of this file, save with Ctrl+o and exit with Ctrl+x.