I can not get my iPhone 8 Plus to work. Error Message iPhone Unavailable after attempted Update last evening

See the following Apple articles:

Update your iPhone, iPad, or iPod touch

https://support.apple.com/en-in/HT204204

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

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

Or update via PC

See this Apple article: Update software on iPhone, iPad or iPod touch in iTunes on PC

https://support.apple.com/en-gb/guide/itunes/itns3235/windows

If you have a Mac see this Apple article: Update your iPhone, iPad, or iPod touch with the Finder

https://support.apple.com/en-us/HT212185