How to forget database

There used to be a command in Commandbox to forget the database, so that I can set a new one.
But I can’t remember the command?

Can you explain what you mean? CommandBox is a CLI tool and doesn’t really do anything with Databases itself. Are you talking about a server started with CommandBox? Or perhaps how to use CFConfig? Or something else??

I’m using it together with preside. When I type “preside start” in commandbox, it asks for the mysql database name.
I would like to change that database.

This is a question you need to ask to the Preside developers. The feature you are using is not a core CommandBox feature, but a custom module they have written on top of CommandBox. @DominicWatson ?

Preside creates a data source called “preside”. You should be able to edit it depending on the CFML engine and additional tools (e.g. CFConfig).