Apologies, I assume too much familiarity with the software. It is with Attribute Manager.
Options > Element Attributes > Attribute Manager
Click on the tab with the Fill icon, on the right side you can 'import' the XML file. If you then select the fill type on the right side you can either append (add it to the bottom of the list in terms of index number) or add by index or by name, which might overwrite an existing fill type in your project.