Blocs comes with a dedicated tool for editing the values and attributes of custom Blocs. The Bloc editor lets you set the title, author, keywords, category and thumbnail attributes for the custom Blocs you have saved and installed.
Access the Bloc Editor
The Bloc editor can be accessed via Developer > Bloc Editor in the main menu.
Beginners Tip
To apply a custom thumbnail to a custom Bloc, simply drag an image that is sized 360x220px onto the image well.