You will need to pass all of the CIMA exams, complete the practical experience requirements and become a CIMA member before you are eligible to become a CGMA.
As a CIMA student, you are already on that path.
The CGMA is a great designation to aim for. As a CGMA, you will extend the global reach of your recognition as a chartered management accountant. Once you become a CIMA member, you are automatically entitled to use CGMA at no additional cost along with all of the other benefits available.