Q: Unable to check for update

Hello Meerutpiyush.

Thank you for using the Apple Support Communities. I see from your post that you aren't able to to check for updates on your iPhone. I'm happy to provide you with some direction to resolve this.

Let's start by making a backup of your iPhone's data. 

How to back up your iPhone, iPad, and iPod touch

Once that is completed, let's our troubleshooting by restarting your iPhone. 

Restart your iPhone, iPad, or iPod touch

If the issue persists after restarting, then let's check if the issue occurs when connected to a different Wi-Fi network. Or using your iPhone's mobile data.

If your iPhone is unable to check for updates on different networks then try updating the iPhone using iTunes on the computer. The steps for that are included in this article under the steps to update wirelessly:

Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support

If you don't have access to a computer then we would want to erase it and set it up as new then try updating. Your data would be safe since you performed a backup at the start of our troubleshooting. Here's an article with the steps to do so:

How to erase your iOS device and then set it up as a new device or restore it from backups

If that resolves the issue, then you can restore your backup. 

Restore your iPhone, iPad, or iPod touch from a backup

Have a nice day.