Installing and upgrading help

I’m a newbie. I installed moodle via softaculous successfully but upon trying to install a theme, I landed on the server check page with changing MySQL to Mariadb

Here is the error: 

database

mysql (5.5.5-10.3.27-MariaDB)

must be installed and enabled Wrong $CFG->dbtype: you need to change it in your config.php file, from 'mysql' to 'mariadb'.

However, in my config.php file I saw : $cfg- libdir / adminlib.php. 

I’m on a VPS server with MySQL. Please can someone please put me through on how to change this to mariadb. Am I supposed to change libdir to mariadb without installing mariadb to the server? 

I got confused because I didn’t directly see $CFG->dbtype in the config.php(I mean I didn’t see MySQL replaced dbtype instead I saw libdir. 

Am I supposed to completely change the database of the server to mariadb? If yes, but I have a long time Wordpress website installed on the same server and I don’t know if changing the database type with the server will cause issues for the Wordpress website. 

Thank you all for reading and willing to guide me accordingly.