The screen of the iPhone and iPad turns almost seamlessly, depending on how you hold it. However, if your display is displayed in portrait or landscape orientation, there are some ways to fix it.
Disabling the registration lock on the iPhone
If your iPhone display is in portrait orientation and does not even rotate in landscape orientation If you hold the handset aside, the portrait orientation lock may be the culprit. Fortunately, we can quickly disable this lock in the iOS Control Center.
If you are using an iPhone X-style device with a notch, swipe down from the top right corner of the screen to view the control center. [1
If you're using an iPhone 8 or earlier with a physical home button, swipe up from the bottom of the screen
In Control Center, locate the icon that looks like a lock with a circle around it. When the portrait orientation lock is on, this icon appears with a white background. Tap the Portrait Alignment Lock button to turn it off.
Below the message "Portrait Align: Off" is displayed at the top of the Control Center.
If you turn the iPhone sideways, your iOS device should switch to landscape orientation.
RELATED: How to Adjust the Control Center of Your iPhone or iPad
Disabling the Rotation Lock on the iPad
Unlike an iPhone, the iPad can be locked in landscape and portrait orientation , For this reason, the feature on the iPad is called a rotation lock.
To disable the rotation lock on the iPad, we use the method described above. Note that the process for accessing the Control Center on the iPad varies depending on the iOS version (or iPadOS version).
If you're using iOS 12, iPadOS 13 or higher, swipe down on the screen in the upper-right corner.
If you're using iOS 11, double-click the Home button to display the App Switcher and icon control panel area on the right. If you are using iOS 10 or earlier, swipe up from the bottom of the screen.
Now tap the Rotation Lock button (the button has a lock icon with a circle) to toggle the rotation lock. Again, when activated, the button will appear with a white background, and when disabled, the message "Rotation Lock: Off" will be displayed.
Restart the app
If you've disabled the orientation or rotation lock and the same problem persists, you'll need to review the app you're using next.
If the app in question is not working or has crashed, you should quit and restart the app. To do this, you must first access the App Switcher on your iPhone or iPad.
RELATED: Troubleshooting Apps Crashes on an iPhone or iPad
If you're using one of the newer iPhones or iPads without the Home button, swipe from the Home Bar up and hold for one second to display the App Switcher. If your iPhone or iPad has a Home button, double-click it.
Now find the app you want to quit and swipe up in the preview.
Locate the app on the home screen and reopen it. If the problem occurred with the app, it should now be possible to turn the iPhone or iPad screen.
Restart the iPhone or iPad.
If the problem persists with multiple apps, then there may be an error on the iPhone or iPad before iPad. In general, such problems are resolved by a simple reboot.
On the iPhone or iPad, using the software launch bar, press and hold the Volume Up or Volume Down button together with the Sideways button to bring up the Launchbar. Slide off to turn off "menu.
For iPhones and iPads with a physical home button, you can display the power-on menu by holding down the Sleep / Wake button. Swipe your finger over the Slide to Shutdown slider to turn off the device.
Then press the "Sleep / Wake Button" or the "Side Button". to turn on the iOS or iPadOS device. While you're at it, you can try to force your iPhone to reboot to see if the problem is resolved.
After restarting the iPhone or iPad, the problem should (hopefully) be fixed.
Reset All Settings  If the problem persists, you can try resetting the iOS or iPadOS settings as the penultimate way out. The last resort is to reset the iPhone or iPad itself.
If you reset all settings, for example, reset Wi-Fi connections and network settings. This is also a great way to fix some quirks and unidentifiable iOS or iPadOS errors – one of them being the rotation lock problem.
Open the app settings and go to General> Reset.
Tap Reset All Settings here.
In the next screen, enter your device passcode to confirm resetting all settings. After restarting the iPhone or iPad, the screen rotation issue should be resolved.
Otherwise, you can use the last-mentioned way out. In the Reset menu, tap Clear all content and settings to get started. When we say the last resort, we really mean it. This option deletes all your personal information and apps. Do not take this step without first backing up.
RELATED: How To Secure Your iPhone With iTunes (And When You Should)