The activity settings on an event level can be changed in the module Activity Management, after selecting an activity you already created. Click on the Settings tab.
Here you can set the status of the activity, whether it is active or not.
You can also choose where to display the activity, this could be the website and/or the Engagement app.
The registration option, once switched on, requires participants to be assigned to the activity in order to participate in it.
You can also choose if you want to use global settings in the Engagement app for this activity. If you turn the switch off you can customize the additional settings for this specific activity. Save the changes.