Reverse auto_increment id existing column in phpMyAdmin
You can create a new table like the old one and insert the values in a different order, for example:

CREATE TABLE new_table like old_table;
INSERT INTO new_table (date, name) 
SELECT date, name FROM old_table 
ORDER BY date ASC, id DESC 


Change the ORDER BY to whatever suits to you- I have ordered by date so it doesn't trust that the original data was right, you can order just by id DESC.

You can later delete the old table and rename the new table as the old table:

DROP TABLE old_table;
RENAME TABLE new_table TO old_table;


It can be done just using a table, but that is easier and lets you check that the contents are ok before changing the original table.

If you did something like this the ids will collide and the query would fail -it would require an additional column or the drop of the PK and two table rewrites instead of one:

SELECT max(id) INTO @maxid FROM my_table;
UPDATE my_table SET id = @maxid - id + 1;