After copy the JSON or Plain Text from your server, you can paste it in
the Configuration and then click Add to finish the WireGuard Client setup.
8.2.2. WireGuard Providers
If you are using Azirevpn or Mullvad, you can click Others and use your AzireVPN
or Mullvad account to set up WireGuard client directly.
AzireVPN: Select AzireVPN as the provider, enter your User Name and Password and then click
"Add" finish the WireGuard Client setup. 
Mullvad: Select Mullvad as the provider, enter your Account Number and then click "Add" to finish
the WireGuard Client setup. 
Waiting for the adding.