You have started your study but are still wondering about what specialization to choose. If you don't know where you want to go, you need to check/ask yourself first: What are your interest areas and what are your work-life goals? You first need to share with us what you want to be or do in your life, which actually matters a lot to you. This will enable us to give appropriate responses.
Also, you are working as an Assistant Service Manager and have good experience, which falls under Customer Relationship and Service Management. Therefore, you can consider pursuing a PG Diploma in Customer Relationship Management from any reputed university. The question is, would you be interested in pursuing this?
If yes, you should consider a Sales & Customer Service course. If not, please share your areas of interest along with your current educational qualifications.