2 Solutions:

1. drop and re-create it

drop sequence seqname;

create sequence seqname start with NEWVALUE ...

(Notice: don't forget about sequence's privilege)

2. alter sequence

alter sequence seqname increment by AVALUE -- (e.g.,expected - currentVal);

- When AVALUE is a positive number,seqname's value will be increased.

- When AVALUE is a negative number,seqname's value will be reduced.