Hey. You can use create or update profile and send it just the email. 

Yes You can use Create or Update profile in the latest stable version of Klaviyo API - 

API: /api/profile-import/
Sample payload:

{
    "data": {
        "type": "profile",
        "attributes": {
            "email": "test@klaviyo.com"
        }
    }
}

​@abhijithvs Are you showing a payload for creating/updating the email address? I think ​@Ray8998 is asking how to do an update without needing the id. I’m trying to do the same thing. For now, I’m doing a lookup using /api/profiles?filter=equals(email,"user@example.com") to get the id.