What I did check documentation, there is no PL/SQL command reset this parameter.
Maybe you contact Oracle support and ask how rest it.
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Login to the database as a user with dba rights (use SYSTEM or SYS for instance) or user APEX_040200
And reset that setting by using this update
update APEX_040200.wwv_flow_platform_prefs set value = null where name = 'RESTRICT_IP_RANGE'; commit;
Login as Sys and change current schema to apex_40200 and run the following script.
wwv_flow_platform.set_preference( p_preference_name => 'RESTRICT_IP_RANGE',
p_preference_value => null );
faced same problem and one of the forum gave this solution, hope it works for you too..