MySQL 8.0

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CREATE TABLE Table1
    (`test_date` datetime)
;

    
INSERT INTO Table1
    (`test_date`)
VALUES
    ('2020-06-10 00:06:17.185449'),
    ('2020-06-10 00:11:05.943217'),
    ('2020-06-10 00:13:45.375109'),
    ('2020-06-10 00:13:45.461321'),
    ('2020-06-10 00:15:32.497548'),
    ('2020-06-10 00:15:32.544873')
;
UPDATE Table1 SET test_date = SUBSTRING(test_date FROM 1 FOR CHAR_LENGTH(test_date) - 7)
SELECT * FROm Table1


test_date


2020-06-10 00:00:00

2020-06-10 00:00:00

2020-06-10 00:00:00

2020-06-10 00:00:00

2020-06-10 00:00:00

2020-06-10 00:00:00