Hey @Isac_Karvia,
I understand your issue you can use this query for your problem according to your table.
CREATE SEQUENCE IF NOT EXISTS items_id_seq;
ALTER TABLE items ALTER COLUMN id SET DEFAULT nextval('items_id_seq'), ALTER COLUMN id SET NOT NULL;
ALTER TABLE items ADD CONSTRAINT items_pkey PRIMARY KEY (id);
SELECT setval('items_id_seq', (SELECT GREATEST(COALESCE(MAX(id),0) + 1, nextval('items_id_seq')) FROM items));
Also check this forum
Primary Key