cant create child attributes

I am using a filter called Countries that displays Brands and then the child brand names. I want to add another brand name to this list but for some reason I can no longer see an option to enter a new attribute brand name as a child of the Brands parent attribute.

Using the link below you will see that there is one stray brand called Manduka which I cant work out how to add to the rest of my brands

https://yogaplanet.co.uk/shop/