Not ever having owned the version you have, I'm just going to imagine that it is generally the same as all the other versions of PE I know, ok? If what I tell you is totally incomprehensible, then chances are probably good that I'm wrong

....
The tool I believe you are looking for is either the 'clone' or the 'brush' ~ in some versions of PhotoExpress, they are both found under the heading of 'Paint', but since I am not familiar with PE 5 SE, I can't tell you
exactly where to find it. But PE is really user friendly, it shouldn't be all that hard to find.
Either one, clone or paint, will open up an options screen. You can use that to decide what area of the original pic you wish to 'clone' onto the damaged part, or to choose your color to paint it with (to pick out a 'matching' color - after clicking "Paint ~ Brush ~ click on the large single colored square and choose 'eyedropper' from the resulting dropdown menu).
Hope this helped ~ good luck!!!
: lobster