basically you have to do this ,
If your iPhone, iPad or iPod touch wonâ  t update
You might be unable to update your iPhone, iPad, or iPod touch wirelessly â   or over the air â   for one of these reasons.
Not enough available storage space on your device
Downloading the update takes a long time
Unable to reach the update server
The update doesn't complete
If there's not enough space to update
If there isn't enough space to download and install an update, the software on your device will try to make space. It will remove only app data that it can download again and doesn't remove or relocate any of your data. If your device still doesn't have enough space, you can use your computer to update your device.
If you can't connect your device to your computer, you can make room for the update by removing content and apps on your device that you don't use. Go to Settings > General > [Device name] Storage.
Learn more about the space your apps and content use.

If the download takes a long time
You need an Internet connection to update your device. The time it takes to download the update varies according to the size of the update and your Internet speed. You can use your device normally while downloading the update, and your device will notify you when you can install it. To improve the speed of the download, avoid downloading other content and use a Wi-Fi network if you can.

If you canâ  t reach the update server or canâ  t verify the update
If you try to update your device, you might see one of these messages:Unable to Check for Update. An error occurred while checking for a software update."
  ð  ´ð  ´Learn how to update your iPhone, iPad or iPod touch to the latest version of iOS or iPadOS â   wirelessly or using your computer.

You can update your iPhone, iPad or iPod touch to the latest version of iOS or iPadOS wirelessly.* If you can't see the update on your device, you can update manually using your computer.

Before you update 
Make a backup of your device using iCloud or your computer.


Update your device wirelessly
If a message says that an update is available, tap Install Now. You can also follow these steps: 
Plug your device into power and connect to the internet with Wi-Fi.
Go to Settings > General, then tap Software Update.


Tap Download and Install. If a message asks to temporarily remove apps because the software needs more space for the update, tap Continue or Cancel. Later, iOS or iPadOS will reinstall apps that it removed. If you tap Cancel, learn what to do next.
To update now, tap Install. Or you can tap Later and choose Install Tonight or Remind Me Later. If you tap Install Tonight, just plug your device into a power source before you go to sleep. Your device will update automatically overnight.
If asked, enter your passcode. If you don't know your passcode, learn what to do.
If you see an error or need more space when updating wirelessly
If you see an error message while trying to update your device wirelessly, learn what to do. If you need more space for a wireless update, you can update using your computer or delete content manually from your device. Whether you use your computer or update wirelessly, you'll have the same amount of free space on your device after you update.
Some software updates aren't available wirelessly. VPN or proxy connections might prevent your device from contacting the update servers.
Update your device using your computer

If you canâ  t update wirelessly on your device, you can update manually using a computer that you trust. If your computer is using Personal Hotspot on the device that youâ  re updating, connect your computer to a different Wi-Fi or ethernet network before you update.
On a Mac with macOS Catalina 10.15, open Finder. On a Mac with macOS Mojave 10.14 or earlier, or on a PC, open iTunes.
Connect your device to your computer.
Locate your device on your computer.
Click General or Settings, then click Check for Update. 

Click Download and Update.
If asked, enter your passcode. If you don't know your passcode, learn what to do.
(* Upgrading to the latest version of iOS or iPadOS software provides the latest features, security updates and bug fixes. Not all features are available on all devices or in all regions. Battery and system performance may be influenced by many factors including network conditions and individual use; actual results may vary.)

if you updated delete YouTube and reinstall it and restart and check
if you canâ  t update youâ  ve to soft reset iPad 
and delete YouTube  and reinstall it and restart or you can watch YouTube in web browser also ð    
*if you canâ  t watch YouTube try another similar apps to watch YouTube 
like your browser
         Or use alternatives
like #1 DailyMotion â  Â YouTube's Laxer Clone.
#2 Vimeo â   The World's Leading Creative Community.
#3 Twitch â   Gamer Heaven.
#4 Vevo â   The Best YouTube Alternative for Music.
#5 Metacafe â   The Hipster's Choice Over YouTube.

 I hope this will help resolve your problem....
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peace