SQL Server 2016

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE #Test
(
    Customer varchar(50) NOT NULL,
    [Fiscal Year] integer NOT NULL,
    [September Amount] smallmoney NULL,
    [October Amount] smallmoney NULL,
    [November Amount] smallmoney NULL
);
INSERT #Test
    (Customer, [Fiscal Year], [September Amount], [October Amount], [November Amount])
VALUES
    ('Customer 1', 2020, $1.23, $2.34, $3.45),
    ('Customer 2', 2020, $4.56, $5.67, $6.78);
2 rows affected

SELECT
    U.Customer,
    U.[Fiscal Year],
    [Month] = LEFT(U.[Month], CHARINDEX(SPACE(1), U.[Month]) - 1),
    U.Amount
FROM #Test AS T
UNPIVOT 
(
    Amount 
    FOR [Month] IN 
    (
        [September Amount], 
        [October Amount], 
        [November Amount]
    )
) AS U;


Customer
Fiscal Year
Month
Amount


Customer 1
2020
September
1.2300

Customer 1
2020
October
2.3400

Customer 1
2020
November
3.4500

Customer 2
2020
September
4.5600

Customer 2
2020
October
5.6700

Customer 2
2020
November
6.7800


SELECT
    T.Customer,
    T.[Fiscal Year],
    U.[Month],
    U.Amount
FROM #Test AS T
CROSS APPLY 
(
    VALUES
        ('September', T.[September Amount]),
        ('October', T.[October Amount]),
        ('November', T.[November Amount])
) AS U ([Month], Amount);


Customer
Fiscal Year
Month
Amount


Customer 1
2020
September
1.2300

Customer 1
2020
October
2.3400

Customer 1
2020
November
3.4500

Customer 2
2020
September
4.5600

Customer 2
2020
October
5.6700

Customer 2
2020
November
6.7800

Customer	Fiscal Year	Month	Amount
Customer 1	2020	September	1.2300
Customer 1	2020	October	2.3400
Customer 1	2020	November	3.4500
Customer 2	2020	September	4.5600
Customer 2	2020	October	5.6700
Customer 2	2020	November	6.7800