Access denied for 'root'@'localhost'

I have installed ERPnext in a fresh VPS Ubuntu 20.04 following this guide.

Everything works fine as explained in the guide. Now I wanted to reset and reinstall erpnext to remove all elements I created for testing using this command:

bench reinstall inside bench directory.

This asks for a mysql root password. But I have never set a root password (following the above turorial). So, I pressed enter. It returns an error “Access denied for user 'root'@'localhost'
I even tried to enter password for the mysql user I created which does not work either.

What might be the problem for this and how can I solve it ?

try bench --site SITE_NAME reinstall --mariadb-root-username MYSQL_USER --mariadb-root-password MYSQL_USER_PASSWORD

this works perfectly. Thank you!