Follow the link https://www.zoho.com/mail/desktop/ to download the Zoho Mail app for Windows.

To Check whether you need to download 32-bit or 64-bit version you can check your system by going to settings/system/about.  Unless you're on a very old machine it's likely that you will need to download the 64-bit version.

Open the downloaded file and follow the instructions on screen.

Enter your .gov.uk email address in the Sign In window:

Then enter your password and follow the instructions for two-factor authentication if you have this set up.

You're now ready to use your email.