Reset change login user name password for nextcloud in a very simple way

First click the password reset link on the login screen; this appears after a failed login attempt. This works only if you have entered your email address on your Personal page in the Nextcloud Web interface, so that the Nextcloud server can email a reset link to you.

Now ask another Nextcloud server admin to reset it for you.

If neither of these is an option, then you have a third option, and that is using the occ command. See Using the occ command to learn more about using the occ command.

$ sudo -u www-data php /var/www/nextcloud/occ user:resetpassword admin

Enter a new password:
Confirm the new password:
Successfully reset password for admin

now try to login using local host or on your System IP http://localhost/nextcloud

Done