Here is a link that I have been using on my iphone but there is a website as well.
This research is led by Dr. Tim Spector professor of genetic epidemiology at King’s College London [he is also director of TwinsUK, a scientific study of 15,000 identical twins and non identical twins which has been running for 30 years]. It is endorsed by all 4 UK Governments and the NHS. It is also supported by many well-known national charities including Versus Arthritis.
One good feature of this app is that you can report for multiple people on the same link.
Help slow the spread of COVID19 and identify at risk cases sooner by self-reporting your symptoms daily, even if you feel well. Download the app
Best wishes and stay safe