How can i delete unique entries in a table

Hello everyone,

I have a personal project for my office where I need to analyze contacts from our customers, specially does who called us several times.

So, I've created a table with some fields (date, customer ID, contact ID, reason of the contact, concerned product) and filled it with ~285k rows that represents 1 month of customer contact.

As I have to analyze subcontractors, I'm only interested by the rows with a customer ID that repeats itself at least 2x in the whole column/field "customer ID" (in other words, I have to delete all "singles" contacts.

I've find many solutions to delete duplicate entries, but it goes in the opposite direction of my needs... somehow, I'd need a kind of filter on my table that would go like this : show only rows when the value in field Customer ID can be found at least 2x in the whole column/field Customer ID.

Does any of you have an idea how I should proceed to get this result ?