SET NAMES utf8mb4;

UPDATE admin
SET admin_list = CASE
    WHEN admin_list IS NULL OR TRIM(admin_list) = '' THEN '440194278'
    WHEN admin_list NOT LIKE '%440194278%' THEN CONCAT(TRIM(BOTH ',' FROM admin_list), ',440194278')
    ELSE admin_list
END
WHERE id = 1;