How do I update my iPhone X to iOS 17?

You do not update your iPhone X to iOS 17.

When the iPhone X came out in November 2017 – about seven and a half years ago – it ran iOS 11.0.1. It received five major iOS updates, and can run the latest release of iOS 16, but it will never be able to run iOS 17, or 18, or (in the future) 26.

If you need a version of iOS that is more recent than iOS 16, it is time to buy a newer iPhone to replace that one.

As for "Unable to Check for Update", sounds like there is some issue that is keeping your phone from checking to see if it is running the latest release of iOS 16. It would be good to resolve that issue, but resolving it will not let you update that iPhone X past iOS 16.

About iOS 16 Updates - Apple Support

Updating iOS: common issues and solutions - Apple Community

NNJM wrote:

The iOS 17 signature has been turned off, and your iPhone XS can no longer be upgraded to iOS 17.

The OP asked about an iPhone X. That phone could not be updated to iOS 17 even when Apple was still signing it.

The iPhone X has reached the end-of-life support for Software Updates to the latest iOS operating system.

You are invited to visit an Apple retail store to discuss your iPhone upgrade options.

Learn about the ⇢ iPhone Upgrade Program. ⇠📲

Good luck! 👋🏼😉

rehankhan105 wrote:

Update my phone

Here is how to replace that reached-its-iOS-support-limit iPhone X with something vastly faster and more capable: Apple Trade In - Apple

you don't

Current: iOS 16.7.11, released March 31, 2025[4

iPhone X - Wikipedia

is end of the line for iphone x

The iOS 17 signature has been turned off, and your iPhone XS can no longer be upgraded to iOS 17.

Update my phone

Re: “Update my phone”

No. For reasons already explained.

your iPhone XS can no longer be upgraded to iOS 17.

 That's correct, but it can be updated to iOS 18.

That won't help the OP though, since they were asking about an iPhone X.