How to Assign a Worker to an Activity:
To assign a case worker to an activity, click on the activity. The activity popup will open and it will show a Case Worker Option. Clicking on this will show the workers which are available for you. You can assign any of them from the drop-down list to the activity.
It will show the list of active workers as shown below.
After assigning a worker. click on the save button. Now the assigned worker will also show on the activity tile as an icon.