Your first step is to think about who you would like to work with next. If you have someone in mind, you can approach this academic informally via email or in person, explain about your research, and ask if they would like to supervise you. If they agree, you can then contact your department’s Postgraduate Coordinator, your faculty’s Vice Dean for Doctoral Studies, or your current supervisor if you feel comfortable doing so, and explain the situation.
If you’re not sure who you would like to work with, then you can contact the postgraduate coordinator or vice dean to ask if they can find someone for you. If you feel comfortable doing so, you can also discuss this with your supervisor or supervisors.
You can talk to your department’s postgraduate coordinator, or your faculty’s Vice Dean for Doctoral Studies. It should be possible to find out who these people are on your departmental website. The Centre for Doctoral Studies also has a list of faculty Vice Deans for Doctoral Studies.