Please help me,

I'm trying to add a timeline to a chart I created (4 years ago) for my boss.

My boss wants me to insert an actual timeline with specific dates (quarterly) along the bottom (horizontal axis) and remove the date text.

I've tried several ways from several different searches, but to no avail. The picture below, shows the best try so far.
chart 2.PNG

I'm sure the answer is something fairly easy, but I'm at my wits end. HELP!!!