Tap the speaker icon on the top right of the screen, then select the volume control options or adjust the volume of the incoming call sound.
If you still do not hear any sounds select the Start Menu -> Settings -> Sounds and Notifications -> make sure that the first 3 boxes for "enabled sounds for" Events, Programs, and Notifications are ALL checked
on the top right of the screen, then select the volume control options or adjust the volume of the incoming call sound.
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