First, try a Soft Reset. Hold the Volume Down + Power buttons until the phone vibrates and reboots (about 10 seconds). Soft Reset is a great go-to to solve many types of glitch. You do not lose user data.
If that doesn't work, check the Store for updates...
Another tactic is to try
SysApp Pusher to see if you can update/recover Settings.
Otherwise you may have to Hard Reset. Power off the phone > hold Volume Down > press Power > keep holding Volume Down until you see the exclamation (
!) screen, then immediately release the Volume Down
Now tap Volume Up / Volume Down / Power / Volume Down
You should see the spinning gears and your phone will reflash the last OS version held in recovery. You do lose data, but get your phone back. Sign into your Microsoft Account and restore your backup during the set up.
Or you could use Windows Device Recovery Tool to reflash the phone. Again, you would lose data, but can restore your last backup. Find that tool here:
How can I recover/reset/restore my phone software? - Microsoft - USA
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