What is the best way to modify Admin Panel on WordPress?

There’s a plugin called White Label CMS https://wordpress.org/plugins/white-label-cms/

I’m not sure if it can do everything you’re looking for, but it’s a start.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)