Is the flowchart inside an anchored or graphic frame? If so, then select the frame and use ctrl-A to select all, then try to click on the arrow to make it the only selection.
If you haven't usd frames, then just do a ctrl+A on the page to select everything and try to select that arrow. WIth a lot of objects in front of it, you may have to de-select the others first (ctrl+click).