In fail2ban 0.10.0 and later, the following command will remove an IP address from all fail2ban jails as well as from the fail2ban database:
$ sudo fail2ban-client unban <IP-ADDRESS>
The old syntax, which required to specify a jail, can still be used to remove an IP from a specific jail:
$ sudo fail2ban-client set <JAIL-NAME> unbanip <IP-ADDRESS>
To view all active jails:
$ sudo fail2ban-client status
To view all IPs in a jail (most recent entries are at the end):
$ sudo fail2ban-client status <JAIL-NAME>
Documentation: manpages.debian.org/unstable/fail2ban/fail2ban-client.1.en