Each App Bloc links to a different service and as such each have slightly different ways to change their content.
For example, if you add a Google Maps Bloc you only need to specify a location as you would via a Google Maps search. Some require you to capture the URL of what you want to link to, eg Sketchfab. The requirements for each Bloc is shown by editing the Bloc.
To help illustrate how to change these Blocs we'll take a look at a Google Map Bloc.
Below we've added a Google Map Bloc and have clicked it to show the edit menu. We've also hovered over the map which indicates it is editable:
By clicking the map we can now edit the location.
To change the map replace Manhattan with your to any location. When you close the overlay the map should instantly be updated to the new location.
This style of overlay is used across many App Blocs. Each has a different requirement, which you should understand if already using these services. You'll find a brief description telling you want's required (URL/Embed Code/IDs etc) to help you out.