You only need a single server certificate , and each clients needs separate client certificates. If you've only handed out 2 client certs I would simply start from scratch.
If you're using the easy-rsa package to set up your certificates then do
. ./vars
./revoke-full <name-of-client-cert>
a so-called Certificate Revocation List file (CRL) will be generated, which you can include in your openvpn server setup using
crl -verify<full-path-to-.crl-file>