Ribbon workbench URL Command Action Parameter Guid

I have a an adress of a dialog form: ...ntityName=opportunity&ObjectId=%wwwww-www-wwww-wwww-wwwwwwww%7d and I want to call this dialog form from a button. I create a button for this and a parameter data in ribbon but and I don't know how to use the parameter data wich the id in the adress: 

Thanks in advance,