-- Table
CREATE TABLE #TempTable (
    Name text,
    UnitID text,
    Country text,
    HS text
)
INSERT INTO #TempTable
    (Name, UnitID, Country, HS)
VALUES
    ('User1',  'U1',  'US', 30),
    ('User2',  'U2',  'AS', 40),
    ('User3',  'U3',  'AS', 50),
    ('User4',  'U4',  'AS', 60),
    ('User5',  'U5',  'AS', 80),
    ('User6',  'U6',  'AS', 90),
    ('User7',  'U7',  'AS', 10),
    ('User8',  'U8',  'AS', 10),
    ('User9',  'U9',  'AS', 20),
    ('User10', 'U10', 'AS', 30),
    ('User11', 'U11', 'AS', 40),
    ('User12', 'U12', 'AS', 70)

select * from schedules where substr(unitIndex, 2, 1) between '1' AND '3'

-- Table
CREATE TABLE #TempTable (
    Name varchar(50),
    UnitID varchar(10),
    Country varchar(2),
    HS int
)
INSERT INTO #TempTable
    (Name, UnitID, Country, HS)
VALUES
    ('User1',  'U1',  'US', 30),
    ('User2',  'U2',  'AS', 40),
    ('User3',  'U3',  'AS', 50),
    ('User4',  'U4',  'AS', 60),
    ('User5',  'U5',  'AS', 80),
    ('User6',  'U6',  'AS', 90),
    ('User7',  'U7',  'AS', 10),
    ('User8',  'U8',  'AS', 10),
    ('User9',  'U9',  'AS', 20),
    ('User10', 'U10', 'AS', 30),
    ('User11', 'U11', 'AS', 40),
    ('User12', 'U12', 'AS', 70)

-- Update statement for all rows between U3 and U10
UPDATE #TempTable
SET HS = 1000
WHERE CONVERT(int, STUFF(UnitID, 1, 1, '')) BETWEEN 3 AND 10

-- Result
SELECT *
FROM #TempTable