The Unity movement and the science of psychology have common roots. Both emerged out of the cultural and scientific mileu of the last half of the 19th century; as such, both place special attention on the mind and understanding how it works. The understanding, put very simply, is that if you understand how your mind works, you can direct its activities in order to attain your goals and aspirations. A simple question is, "Can I control my mind." Well, to be frank, its not a simple question.
First of all, we have to ask who is the the "I" that is asking? Secondly, it is imperative to get a clear definition of the word "mind." I'll begin with the latter question. The term "mind" is often considered to be made of three parts: the conscious mind, which is the assemblage of all the thoughts, feelings and reflection we are aware that we are aware of. The second is the subconscious mind, which is the assemblage of all the memories, feelings, etc. of which we are not consciously aware. We often expeirence these through our dreams. The third is the superconscious mind, the assemblage of what we in Unity call divine ideas - the best and highest of which we are capable.
To answer the former question, "Who is the 'I' that is asking" we have to be open to any number of answers. "I" might be my current personality; "I" might be the Christ within; "I" might be the dispassionate Observer self. And that's just a short list. Most people, I think, would tend to answer that the "I" is my personality, with all its strengths and challenges.
So, could the "I" of personality control the three phases of mind? I would have to say no. However, this "I" could exert great influence on the conscious phase; become more aware of what is in the subconscious; and open itself to the divine possiblities of the superconscious phase. With spiritual education and by adopting spiritual practices, this "I" could improve its capacity to realize the truth of its own inherent divinity - the Christ within - thereby, again, enhancing its influence on the mind. Like a never-ending helix of spiritual evolution.
The above is an exceedingly short answer to a highly complex, though simply looking question. As individuals on a spiritual path of unfoldment, answering this question will be part of our life's work. Fortunately, we have all the time and all the resouces we need to answer it.
Peace be with you and namaste!