@sanyan
you can apply for a master's/diploma in psychology if you have graduated from any of the connected disciplines like History, Sociology, Medicine, Philosophy, Social Work, etc.
Even if you are not a graduate from a connected discipline, some universities offer such students a pre-masters course in psychology. They can take up that course and then go for their masters.
You can always connect with the right counselors who can guide you about how to begin the application and other processes.