Openvpn revoke: how to do it?
Solution 1:
Usually removing the client key should be sufficient for to deny access but there might be configurations where this is insufficient.
In order to easily test it you could create a new client and make sure you can connect with it. Afterwards remove the key of the new client and try again to connect. If you're unable to my assumption would be that removing the key is sufficient.
In the long run you probably should spend some time to document the current system and dig into how it is setup.