You cannot. We cannot and will not support old installations of Virtualmin (and repos for old installer versions are periodically deleted to prevent people from using old unsupported versions). (And, how the hell did you interpret my comment there as being a suggestion to install an old version of Virtualmin?)
Switching to MySQL is covered in several other posts in our forums (be careful about who you take advice from, as well…if it isn’t me or other staff, maybe keep reading for follow ups from one of us). If you insist on doing so, you should do some homework first.
In short:
- Install MySQL server and client from system provided packages, not third party packages unless you cannot avoid it. If you must install from third party repos, you must configure Webmin to know where to find the configuration and other support files. Never install anything from source code on a production server.
- Install Virtualmin. This should detected the already installed MySQL packages and not install Mariadb.
You’re probably done. Double check to be sure the MySQL module recognizes that you have MySQL and not Mariadb (there may be some cached names in the menus, but those are all cosmetic…the same Webmin module is used for both MySQL and Mariadb because they are almost identical from a user perspective).
I want to be clear you almost certainly should not do this. But, this is how you do it, if you must.