Well that’s an interesting one… there are bound to be courses available in accounts management and dealing with customer service etc, but I am of the opinion that experience is 10 times more valuable than a certificate.
I would suggest that you get involved in something outside of work to gain the extra experience. Perhaps you can get in touch with your local estate agent or volunteer your services to a letting company and gain some experience (and contacts that way).
Have you actually tried applying for jobs in the field that you are interested in? As it may be companies will recognise your skills and potential and be prepared to train you in the skills which need developing.
Good luck.