I do not have the App Store

The usual reason for it not being visible is due to a restriction on purchasing. See: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

If that is not the cause, try using Search to see if that will locate it: Use Search on your iPhone, iPad, or iPod touch - Apple Support

If necessary, 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.