iOS 13.7 lets you opt-in to the COVID-19 Exposure Notifications system without the need to download an app. System availability depends on support from your local public health authority. For more information see covid19.apple.com/contacttracing. This release also includes other bug fixes for your iPhone.
Some features may not be available for all regions or on all Apple devices. For information on the security content of Apple software updates, please check the details in the link below:

https://support.apple.com/kb/HT201222

To update it, just go to Settings > General > Software Update or update it from iTunes.