How to view pre-trigger data on digital scope (Owon SDS-7102)
You see the little purple jigger at the top of the screen? That shows where the trigger point is in the scope's trace memory. What you want to do is use the horizontal knob to move that to the right, then take another sample. Then use the zoom function to examine the area just before and just after the trigger point. Alternatively, start with a fairly long time base, and get a feel for just how long the connection period is. Then, decrease the time base until the period mostly fills the screen. The problem with doing it this way is that, if something happens after the trace period, there's no way for you to know it.

With  the trigger point all the way to the left (in what's called the display window) only data acquired after the trigger event will be displayed. If you move the trigger point all the way to the right, only data acquired before a trigger event will be displayed. Notice that in the manual, the "normal" setting is in middle of the window, although this is obviously adjusted depending on what's important to you.