Video Source: Spiritual Awakening
The Solar Plexus Chakra being the third chakra corresponds to this 3rd density of existence. You can therefore use its energy to improve your manifestation skills. In this video, Nicky Sutton clearly describes how to use your Solar Plexus chakra to magnify your ability to manifest your intentions.
Note that Charles Hanaal, author of The Master Key System (one of the most important books ever written about the law of attraction), also says that the solar plexus is key:
The solar plexus is the point at which the part meets with the whole, where the finite becomes Infinite, where the Uncreate becomes create, the Universal becomes individualized, the Invisible becomes visible.
Read more about The Master Key System here: