First you would need to pick out a mid-range theory and a grand nursing theory. Having chosen those will make searching in the library easier. There should be some listed in your textbook. Below are links to two websites that have a list of grand and mid-range nursing theories. Mind you, this is simply a place to look for nursing theories but not something to quote or reference.
For this example, Jean Watson's Theory of Human Caring will be used. It is a Grand Theory. You can simply search for the theory, like this: