When an IP is banned by Fail2Ban and you want to un-ban that IP, the command you need to run is:
sudo fail2ban-client set <jailname> unbanip ipaddress
You can get the jailname by running:
sudo fail2ban-client status
If you want to find what IPs are banned by Fail2Ban, you can check the IPTABLES by running:
sudo iptables -L -n
An example output would be:
Chain f2b-sshd (1 references) target prot opt source destination REJECT all -- 188.29.164.197 0.0.0.0/0 reject-with icmp-p ort-unreachable(1 references
To unban IP 188.29.164.197 from the sshd jail, the command would be:
sudo fail2ban-client set sshd unbanip 188.29.164.197