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The blocking is done by adding the offending IP to a number of iptables filters.
To enable yourself to log in again, the first thing you need is access to the machine. This initially sounds a bit like There's a hole in my bucket, but usually you can get in via another PC.
How can I remove an IP address that Fail2Ban blocked?
iptables -L -n --line-numbers
Find the line numbers and chain names of your IP then:
iptables -D CHAINNAME X
where CHAINNAME is the name of the chain and X is the linenumber of the rule you wish to remove, eg:
iptables -D f2b-sshd 1