How to run two tasks in a single task

Hello I have a task and i used a start process activity for the application then application started process and its running as per the condition the next step is to run script after successful completion of application processing but in UI what’s happening is. it is not waiting for the activity to completes and it is executing in sequence. so it should not be in my case. I used activities called Imgae exists and on image vanish and wait image vanish all are done and even delay is also not working. developer please advise.