Hi,
Sound Forge is a two track editing program, so it does not have a multi-track view.
If all you want to do is add the encores to the end of the 1st set you can do a copy and paste. Just open the encore and the 1st set. Go to the encore window and select all. Click copy. Go back to the 1st set window. Make sure your cursor is at the end of the first set and click paste. I generally create a region for both the 1st set and the encore to make it easier for me to find the point of the cut and paste, and make sure there is no audible click.
There are some other options depending on what version of Sound Forge you are using, but a copy and paste is probably the simplest.
I hope that helps.
Take care,
T.