The esmvaltool command is provided by the ESMValCore package, the documentation on configuring ESMValCore can be found here. In particular, it is recommended to read the section on the User configuration file and the section on Finding data.

To install the default configuration file in the default location, run

esmvaltool config get_config_user

Note that this file needs to be customized using the instructions above, so the esmvaltool command can find the data on your system, before it can run a recipe.

There is a lesson available in the ESMValTool tutorial that describes how to personalize the configuration file. It can be found at this site.