You can use the OpenVPN Connect App available in the App Store for iOS Devices - OpenVPN Connect on the App Store (apple.com)
Download and Install the app.
Make sure you have the Files App installed on your iOS Device which is made by Apple - Files on the App Store (apple.com)
Login to your account at https://vpnpro.uk/login
Select Downloads, and download the vpn server profile you would like to connect to.
Open OpenVPN Connect App and make sure you select Import From File.
Choose the file you downloaded, and enter your vpn username. Tick the box Save Password, and enter your vpn password.
Press Add and the server profile will be saved.
Simply press the toggle on the server profile to connect to the VPN Server.
You are now connected.