Get the repeated count of users


I am trying to get the "revisited users in a span of 7 days". I have a session table in dynamo DB which has the userId field. I need to get the total count of userIds which are repeated. I tried in Visual Builder and 42 Metric with JSON input {"min_doc_count":2}, but couldn't get the unique count of users which are duplicate. Is there any direct filter which can give me the required result in Kibana visualization?
Please help me.