GEAR KNOB GAP

2005 I have 206 hdi tools. There is a problem in my car that is not serious, but it bothers me. & Nbsp; While in gear, it shakes as if it is in neutral gear. (Think about how it shakes when I wasted) I hit the gear like a small slap and it makes it right and left 3-4 times. What can I do? What are your solution suggestions? and how much does it take me to get it done? & nbsp;