If it isn't showing in both Icons and in "Settings", "Apps", "All", then either it is gone, or it is being hidden by something that is on the tablet.
Try starting up in "Safe Mode". If it shows up there (while you won't be able to use it in there, you can see if it is there). If they show, then there is a bad app, virus, malware, etc., on the tablet that needs to be removed. If they still don't show, even in "Safe Mode" then they were removed from the device and would have to be re-added.
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.