First, in the Send Item activity fill out the Item Destination panel. The first field is the Item object where the created object will be placed. The second field is the Activity ID of the activity that you want the item to start later on.
When this activity happens it creates a new item in the specified destination and adds 2 labels to it. First, a Patient label that refers back to the patient who created it. Second, an Activity label that holds the Activity ID you specified above.
Second, at the point you want the item to trigger the patient's activity, add the Start an Activity trigger instruction. For example, in the attached model, this pickoption was added to ItemExit1's On Entry Trigger. By default, the code is configure to use the Patient and Activity labels on the item:
Third, clear the Predecessors field of the activity you want the activity to start.