Which Solus desktop are you using?
Download the openvpn files, skip step 2 "Install and set up the VPN with Network Manager" & step 3 "Connect to the VPN": https://www.expressvpn.com/support/vpn-setup/manual-config-for-linux-ubuntu-with-openvpn/#download
Extract the files to where you want them, could be /etc/openvpn (you will have to create the folder).
In Solus Budgie you do this:
1) Left click on the network manager.
2) Hold the mouse over "VPN Connections" then click on "Configure VPN".
3) Click on "+", click on the drop down menu and choose "Import a saved VPN configuration", then click "Create".
4) Choose one of the openvpn files you downloaded, if you put them in /etc/openvpn you need to navigate there.
5) In the window that is now showing, under "Authentication" you need to enter "User name" & "Password", then click "Save".
7) Connect to your VPN by clicking on the network manager icon, then "VPV Connections" and choose the VPN connection you just set up, which is now listed above the "Configue VPN" text.
That should be it... it is pretty much the same for every VPN provider, if you can download the openvpn files from them.