Freeform Element Connections to Update Existing Entries
According to the Freeform docs it looks like you'll need to pass an element ID.

Freeform allows you to edit/update existing Craft elements (Entries, Users and Calendar Events currently) by including the elementId parameter in your form. It works by feeding a Freeform form an element ID.

{{ craft.freeform.form(&quot;editCraftUsers&quot;).render({
    elementId: currentUser.id
}) }}

The docs have more details on the exact options.