See details on this NHS site:The new NHS COVID-19 app, available to download for free in England and Wales from 24 September, is the fastest way to see if you're at risk from coronavirus. The faster you know, the quicker you can alert and protect your loved ones and community.
The app has a number of tools to protect you, including contact tracing, local area alerts and venue check-in. It uses proven technology from Apple and Google, designed to protect every user’s privacy.
This link takes you directly to an explanatory video:
If you choose to go directly to Apple's App Store, you can search for:
..and download the app directly to your iPhone.
It requires the latest IoS version.
This download worked as at 23:45 on 23 September.