lostpassword page

One option is to change it to phpmyadmin.

Here is a tutorial on 2 ways to change your password, 1 is with the database:
https://blondish.net/articles/tutorials/two-ways-to-retrieve-your-wordpress-password/

you could also change your username of admin in the database too! –

update tableprefix_users set user_login=’newuser’ where user_login=’admin’;

set newuser to the username to what you want it to be.

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As for allow only email and not username in the lost password page, I am sure you probably could alter the code in your wp-login.php in the section under “Handles sending password retrieval email to user”.

I know how to change the username from admin in phpmyadmin.
But is it dependant by some plugins using the keywords ‘admin’ ?

if ($username == 'admin')

it should not be at all as the plugins should not be asking anything other than the general variable ( example: $username ) and not what your username actually is.