CREATE TABLE T
    (`user` varchar(4), `sales` int, `reference` varchar(400) DEFAULT NULL, `quantity` float DEFAULT NULL, `orders` int)
;

INSERT INTO T
    (`user`, `sales`, `reference`, `quantity`, `orders`)
VALUES
    ('xx01', 100, '[{"productid":"80000052","quantity":"1","reference":"ML-41"},{"quantity":1,"reference":"ML-32","productid":"ML-52"},{"productid":"80000052","quantity":3,"reference":"ML-11"}]', 0, 0),
    ('xx02', 200, '[{"productid":"80000052","quantity":2}]', 0, 0),
    ('xx02', 400, '[{"productid":"80000052","quantity":3}]', 0, 0),
    ('xx03', 300, '[{"productid":"80000052","quantity":4}]', 0, 0),
    ('xx03', 500, '[{"productid":"80000052","quantity":5}]', 0, 0)
;

UPDATE T t2,
( SELECT sales, quant FROM T, JSON_TABLE(T.reference,
    "$[*]" COLUMNS(
        quant VARCHAR(400) PATH "$.quantity"
        )
    ) AS jt1
) t1
SET t2.quantity = t1.quant
WHERE t1.sales = t2.sales;