During the running of a slideshow, if you accidentally click on a screen too far, how do you click back to the previous screen please?

Hi Catherine, Thanks for the post, welcome to the forum, in 2007 as in any of the versions of PowerPoint, there are a whole raft of ways to navigate between slides, I find that I tend to use the N key for next and the P key for previous, You could also use the forward and back keys, the page up and page down keys on your keyboard, and then if you want to you can use the mouse; if you right click on the screen and from the menu option which pops up choose Previous slide.
Sorry but there are a lot of ways to do what you have asked. Hope that lot helped, best regards Pete