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