MariaDB 10.5

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CREATE TABLE users (
  `login` VARCHAR(7),
  `regdate` VARCHAR(20) ,
  `ordering` INTEGER
);

INSERT INTO users
  (`login`, `regdate`, `ordering`)
VALUES
  ('user', '1633205589', '1'),
  ('guy', '16332060000', '3'),
  ('account', '16332090000', '2'),
  ('data', '16332095000', '4');

Records: 4  Duplicates: 0  Warnings: 0


UPDATE users  u1
JOIN (SELECT `login`, `regdate`, row_number() over (ORDER BY regdate ASC) rn FROM users) u2 
ON u1.`login` = u2.`login` AND u1.`regdate` = u2.`regdate`
SET u1.ordering =  u2.rn ;

Rows matched: 4  Changed: 2  Warnings: 0


SELECT * FROM users


login
regdate
ordering


user
1633205589
1

guy
16332060000
2

account
16332090000
3

data
16332095000
4

login	regdate	ordering
user	1633205589	1
guy	16332060000	2
account	16332090000	3
data	16332095000	4