For ProtonVPN as an example: you can go to the downloads section and download the wireguard config you want and then import it from the wireguard gui.
For me, I would never use other inferior VPN clients after knowing how efficient, supported and developed are the official Wireguard gui are.
Other providers who provide configs:
Did they get their account back but not the others? What makes you suspect that Windscribe specifically is compromised?
Those three were all locked out within a day. Attack was probably some specific target. The timing is just super suspicious