“Can you refresh my memory?”

You're talking with your friend from high school about other people who used to go to school with you. Your friend asks if you remember a certain person, but you don't really remember that person. You want your friend to give some more information about that person to help you remember. You ask:

Can you refresh my memory?

refresh (someone's) memory

This phrase means to remind someone by giving them more information or reviewing something that they should already know.  It can be used in both casual and polite conversation.