Swipe down on your Home Screen and search for App Store
Check your App Library for the App Store app
Go to Settings
Tap Screen Time
Tap Content & Privacy Restrictions
Tap iTunes & App Store Purchases
Tap Installing Apps
Select Allow
Go to Settings
Tap General
Tap Transfer or Reset iPhone
Tap Reset
Tap Reset Home Screen Layout
Check for an App Store restriction in Screen Time
Restart your iPhone
Update your iPhone to the latest iOS version
If App Store is still missing, contact Apple Support