get the sequence have created

select * from all_sequences;
select * from user_sequences;
select * from dba_sequences ;

view trigger on table

select trigger_body
from user_triggers
where triggering_event = 'INSERT'
and table_name = 'YOUR_TABLE';

How to Reset a Sequence in Oracle

create or replace

procedure reset_sequence(p_seq in varchar2)

is

    l_value number;

begin

-- Select the next value of the sequence

    execute immediate

    'select ' || p_seq ||

    '.nextval from dual' INTO l_value;

-- Set a negative increment for the sequence,

-- with value = the current value of the sequence

    execute immediate

    'alter sequence ' || p_seq ||

    ' increment by -' || l_value || ' minvalue 0';

-- Select once from the sequence, to

-- take its current value back to 0

    execute immediate

    'select ' || p_seq ||

    '.nextval from dual' INTO l_value;

-- Set the increment back to 1

    execute immediate

    'alter sequence ' || p_seq ||

    ' increment by 1 minvalue 0';

end;

/

source http://www.oratable.com/reset-sequence-in-oracle/