It’s not working I can’t install the update it keeps say error

Can you post a screenshot of the whole screen, it could reveal why you aren't able to update.

Make sure you:

• Are using a WiFi connection (not a hotspot).

• You have an active cell signal

• Have your battery charged at least 50%. Better yet, keep it plugged in during the update.

• Are not using a VPN connection.

• Do not have power save mode turned on.

• Do not have a beta version installed.

• You have at least 6 gigs of storage available.

You can also check out this article for help -

If your iPhone, iPad or iPod touch won’t update

https://support.apple.com/en-gb/HT201435

A "no service message" indicates an issue with your cell service. You will need to contact your cell carrier and work with them to fix that. You also need to have a WiFi connection to do the upgrade, or plug into a computer and upgrade through iTunes.

You will need to correct both those issues before you can upgrade.

You need to have both WiFi and cell service to update the iOS.