PL / SQLブロックに入れる必要があります:
declare
videoID number;
begin
insert into VM_VIDEO (VIDEO_ID, ...)
values (SEQ_VMMIGVIDEO_ID.NEXTVAL, ...)
returning VIDEO_ID into videoID;
insert into IMAGES (IMAGE_ID, ...)
values (SEQ_IMAGE_ID.NEXTVAL, ...);
update VM_VIDEO
set THUMB_IMAGE_ID = SEQ_IMAGE_ID.CURRVAL
where VIDEO_ID = videoID;
end;