Un-revoke openssl client certificate


by my mistake I revoke one openssl client certificate.
Is there any way how can I un-revoke this certificate again?
I know it is easier generate new client certificate but problem is I have no direct access to two devices using this certificate and I am not able change on these devices the certificate to new generated certificate anyhow anytime soon. When they are able connect with the same certificate to VPN again I can managed devices again.
On these devices there is a daily reboot at night set in cron so after restart it should connect to VPN automatically again.
in /etc/ssl/ca/openvpn/index.txt I changed R to V and delete the timestamp
it is not enough