The Harvst web app will be the way you interact with your control box most of the time. Changes to settings on the web app will be collected by the control unit next time it does its half-hourly update.
You can access the web app anywhere, on any device, at https://grow.harvst.co.uk ... there's nothing to download.
Once you have signed up for a web app account, you will be guided to assign your control unit to your account.
If you are close to your control unit, you can also access it via the device dashboard; the same place you configured the WiFi settings. Changes to settings here will take effect immediately on the control unit, and will be pushed to the web app next time the system does its half-hourly update.
Use the device dashboard for immediate tasks such as "water now".