The UK government and the NHS provide detailed advice for any action you should take after your COVID-19 Coronavirus test.
What your Coronavirus test results mean and what you should do next
https://www.nhs.uk/conditions/coronavirus-covid-19/testing-and-tracing/what-your-test-result-means/
How test and trace works
https://www.gov.uk/guidance/nhs-test-and-trace-how-it-works