Question Need assistance adding or binding a button to a prefab

In my AR app, I am trying to have a button always located to the top corner of a prefab. I got the prefab from the asset store. This is my first time using assets from the asset store so I am not familiar with working with just the prefab and not the original object. How could I do this? Would I need to create a new canvas with the prefab in it and a button above the prefab, an then use the new canvas instead of the prefab?