How to get AppStore again

The App Store is not one of the apps that can be deleted. The usual reason for it not being visible is due to a restriction on purchasing. See: https://support.apple.com/en-us/HT201304#prevent-purchases

If that is not the cause, try using Search to see if that will locate it: https://support.apple.com/en-us/HT201285

If the above doesn't work, do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.