We have a Blackburn Delphi 3.0 on an indoor stationary bike. I am trying to change a battery - first time. Manual online says how to open the battery door but how do I get to the battery door. someone else did the installation & it worked fine - just needs CR2032 3v Lithium Battery. I am afraid to pull the unit apart to look for the battery door. I don't know where to pull or if there is a button I should be pressing before I start pulling. Unexperienced in such matters.