dropdown box populate all values in datagridview r selected

Question

I want to select values in a datagridview.

then select a value from a dropdown box

then press a button and have the value selected in the drop down box populate all the values that were selected (highlighted) in the datagridview.

 

I am using c# winform application. 

 

Thank you in advance for any help. I've been trying to search all over the web and unable to find a way to do this. Thank you again.