ability to chose the trigger's selector

Since the Animate CSS Block module adds animations to a block's settings form based on the configuration options of the Animate CSS module, it uses the block’s default system ID as the selector. Therefore, an additional input field for specifying a custom selector isn’t necessary in the block's settings form.

However, if you're using the Event option in the block animation settings and require a more specific selector for triggering the event, you can modify it after saving the block settings. Simply navigate to Administration > Structure > Animate List at the path admin/structure/animatecss, and there you can update the saved block's selector.

Please let me know if this solution resolves your issue.