How to rotate asus tablet webcam display 90 degrees?

The settings icon is what you want to use, then display. There is the setting for when the screen rotates (i.e. shaking, turning etc.).
But individual apps may decide that they want to turn this facility on or off.

You should be able to just turn the tablet on its side an the screen would auto rotate but if not go to settings an select screen settings/display an change the setting to auto rotate.

On your tablet, go to the application drawer and open Settings. Tap on Display, then check on uncheck the box for Rotation.

Go to settings>display and make sure the autorotate is enabled. If it still isn't working then there may be an issue with your device's accelerometer, test it in a game such as temple run.

Make sure you have enabled screen-rotation in your tablet settings.

You may want to try double-tapping. In most programs this will zoom back out.

No reset is necessary to fix this problem. Screen rotation is a typical feature on many laptops.
To rotate the display on the screen 180 degrees, simply press CTRL, ALT & down arrow on your laptop's keyboard.

press ctrl+alt+up arrow key (Try any arrow key to rotate it). Usually, it is the shortcut key combination for screen rotation

Use CTRL +ALT+ (Arrow keys)to rotate the screen.

on the front of the toughbook there are 4 small buttons, the 3rd from the left which has a right angle symbol with a double headed arrow in it rotates the screen 90 degrees each time you press it. this is probably how you got it like that in the first place.