Unless you are going to use the system of evocation laid out within the book, you can skip directly to the part about Saspu. However, you may want to note down the banishing incantation which you should find in the section that talks about the circle and triangle (it’s also here on the forum).
The square will be on the page with the name of the kingdom. If I’m not mistaken, you will find Saspu in the Red Kingdom which is presided over by the Grand Spirit Lotir.
The angels in KoF are a bit different from the usual archangels, more fiery, so I’m not sure if that incantation to connect with the angelic frequency will work for them, but you can try it. I would use the banishing incantation first though, before using it so you don’t inadvertently cancel it out.
@SilentSeeker Saspu is an Angel of Love and Friendship.