I have solved this issue. Thanks to the youtube tutorial here by ArcadEd -----> youtube.com/watch
In that tutorial, the example shown is for tiled background but the events works if you going to have a single tall sprite like what i'm trying to do. My event here is as below
My background sprite for now is not that big as its currently just a placeholder so the timer to wait for 30 secs is the estimate time for the sprite to travel at the gamespeed of 25 before it goes out of screen.
So after 30 seconds, set bulletspeed to 0 and stop the travel.
Thanks all who contributed and viewed and also to ArcadEd for your videos.