Split rows and assign a specific value to each group
WITH cte AS ( SELECT Customer_id, NTILE(4) OVER ()::TEXT "Value" FROM customers )
UPDATE customers
SET "Value" = 'dos-' ||  cte."Value" || '-' ||  cte."Value"
FROM cte
WHERE customers.Customer_id = cte.Customer_id;


fiddle

PS. It's recommended to use some ORDER BY in OVER clause (for example by Customer_id) - without it the result is not deterministic...