You can access your App Sharing Settings by pressing the Users icon at the bottom of the navigation bar.
Here you can set the level of access for your Workspace Users for a particular app.
When creating an app, you are asked to choose whether all workspace members were users or whether you kept the app private. You will see that the app sharing settings reflect this choice.
From here you can change these settings - you can update the level of access that all workspace members have or you can change the Role of a specific person (for example you can make someone an admin of the app).
For further information on Inviting/Managing Users and how to configure additional Roles, see the linked section below: