To add custom fields to locations of the training events, log in as an administrator to your system and from your Administration dashboard visit the Extend Profile section. 

To add a new profile field click on the button 'Add Field' on the top left corner of the screen (1).

Fill in the field properties, such Name, Label, etc and for the option 'Create for' choose Locations (2).

Once you have created your new custom field for courses, it will appear in the list of all available extended profile fields.

From now on, when you add or edit a location this field will appear among the location's advanced settings (3).