Is this in an app, or in the settings? As it should actually 'auto rotate'. If none of the following will work, then you would have to get the device repaired to get access.
Option 1...
Restart the device. Sometimes this is all it needs.
Option 2...
1. On the home screen, "Swipe" down the "Notification Bar" at the top of the screen.
2. Tap “Screen rotation” to turn it off/on.
If you don’t see, “Screen rotation” when you go into the "Notification Bar", you may have to swipe "Left" on the selections. You can also tap the "Edit" button at the upper right corner to add the button.
Some tablets may have the option under “Settings”, then “Display” and finally “Screen rotation“.
Option 3...
1. From the home screen, tap and hold the...