MySQL 8.0

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select version();

version()

8.0.30

CREATE TABLE users
    (`created_at` varchar(20))
;
    
INSERT INTO users
    (`created_at`)
VALUES
    ("06.01.2020 8:10"),
    ("07.01.2020 8:10"),
    ("08.01.2020 8:10"),
    ("09.01.2020 8:10")

Records: 4  Duplicates: 0  Warnings: 0

SELECT STR_TO_DATE(created_at, "%d.%m.%Y %k:%i") FROM users;

STR_TO_DATE(created_at, "%d.%m.%Y %k:%i")

2020-01-06 08:10:00

2020-01-07 08:10:00

2020-01-08 08:10:00

2020-01-09 08:10:00

UPDATE users SET created_at = STR_TO_DATE(created_at, "%d.%m.%Y %k:%i");

Rows matched: 4  Changed: 4  Warnings: 0

SELECT * FROM users;

created_at

2020-01-06 08:10:00

2020-01-07 08:10:00

2020-01-08 08:10:00

2020-01-09 08:10:00

ALTER TABLE users MODIFY created_at DATETIME

Records: 4  Duplicates: 0  Warnings: 0

SELECT * FROM users;

created_at

2020-01-06 08:10:00

2020-01-07 08:10:00

2020-01-08 08:10:00

2020-01-09 08:10:00