1. Download and install the SoftEther VPN Client from https://www.softether-download.com/
You will need to select
SoftEther VPN (Freeware) -> SoftEther VPN Client -> Windows (or Linux/macOS) -> Intel (x86 and x64)
to get the latest download link.
2. Download this configuration file and open it. When you connect it will prompt for admin to install the adapter. Afterwards it will ask for a password that you should know.