You can use this commando shell to modify the entrance in the IP tables and to generate a rule

IN ORDER TO UNBLOCK AN IP THE USA THE FOLLOWING EXAMPLE
iptables - I INPUT - s 189.216.139.148 - j ACCEPT

IN ORDER TO BLOCK AN IP YOU CAN USE THIS EXAMPLE
iptables - I INPUT - s 189.216.139.148 - j DROP

IN ORDER TO ELIMINATE A RULE OF TABLES IP
iptables - F

IN ORDER TO LIST THE RULES OF TABLES IP
iptables - L - n