My iPhone 6s doesn't have AppStore

Check if it's restricted: Settings > General > Restrictions. If "Installing Apps" is off, you won't see the App Store.

If that doesn't work, try going to Settings > General > Reset > Reset Home Screen Layout.

If Restrictions password is set (somehow) - then it is very likely stevejobsfan0123 surmise is correct

Thee is no way to recover a restrictions password - you will have to restore to factory conditions

If you restore from backup the restrictions password comes right back

Use Restrictions on your iPhone, iPad, and iPod touch - Apple Support

Get help

When you have Restrictions on, you might notice that you're missing a particular app or feature, such as:

• You don't see an app on the Home screen (like Safari, Camera, or FaceTime).
• You can't use a certain feature or service (like Siri or Location Services).
• You see that a setting is missing or dimmed (like Mail, Contacts, and Calendar; iCloud; Twitter; FaceTime).

If you're missing an app or feature, try turning Restrictions off.

If you lose or forget your Restrictions passcode, you'll need to erase your device and then set it up as a new device to remove the Restrictions passcode.

Import your photos to your computer: iOS: Importing personal photos and videos from iOS devices to your computer

Some other things, like contacts and notes, sync via iCloud and won't be lost when you restore.

Backing up won't do you any good at all. The ONLY way to get rid of the restriction passcode is to wipe the phone and set it up as a new device. You can NOT restore your backup. If you do, it will put the restrictions back in place and you'll be right back where you started from.

Extract the pictures to your computer before you wipe it, then. Or email them to yourself... whatever you want to do... but doing a backup will accomplish nothing since you will NOT be able to restore the backup without landing in the same boat you're in now.

Settings > General > Reset > Reset Home Screen Layout. App Store is part of the iOS and will appear on 1st page of home screen.