The edit dialog for Button Nav templates is accessed by an option added to the block edit menu. To use Button Nav with an autonav or other supported block or stack:

1. Add the block to your page or global area as you normally would
2. Select the Button Nav Dropdown block template
3. The block edit menu will now show an additional options for Button Design
4. This pops up a dialog to input and associate a button design with the block.

See Getting Started - Edit Dialog for more details.

Please read the full Documentation and Examples.