I can´t install phpmyadmin in a wordpress multisite

I need to change the ip address of the droplet to an actual domain in a wordpress multisite. I´ve pointed the domain to digital ocean and created the domain records in the droplet, but now after typing the domain name in the browsers, automatically gets the ip of the droplet. So i´ve read some tutorials on how to fix that, and supposedly I have to alter some columns in the database.

I´ve tried by SSH but I finally couldn´t. Now I´m trying to install phpmyadmin but I´m getting the following error:

ERROR 1045 (28000): Access denied for user
│ ‘debian-sys-maint’@‘localhost’ (using password: YES) . Your options are:
│ * abort - Causes the operation to fail; you will need to downgrade,
│ reinstall, reconfigure this package, or otherwise manually intervene
│ to continue using it. This will usually also impact your ability to
│ install other packages until the installation failure is resolved.
│ * retry - Prompts once more with all the configuration questions
│ (including ones you may have missed due to the debconf priority
│ setting) and makes another attempt at performing the operation.
│ * retry (skip questions) - Immediately attempts the operation again,
│ skipping all questions. This is normally useful only if you have
│ solved the underlying problem since the time the error occurred.

Could someone tell me how is the easiest way to modify the database to change the current ip of the droplet to an actual domain to set the main domain of the wordpress multisite?

Thanks