Short answer: You can’t cause of the way EOS works.
Long answer: You have to run at least 3.6 to have the Toolbox technology available, then create a new container and install MySQL (MariaDB) in it.
toolbox create
toolbox enter
sudo bash
dnf upgrade
dnf install mariadb mariadb-server
This will install the needed components. Then you have to run and configure it:
systemctl start mariadb
mysql_secure_installation
Note that MySQL isn’t available in Toolbox (it’s a Fedora 29 running inside the container), but MariaDB is. Should be no issue tough. Additionally, you need to start MariaDB each time you boot up your host:
toolbox enter
sudo bash
systemctl start mariadb