this is from the documentation:
It is not possible to merge 2 $user_ids together using the Simplified API. We don’t recommend doing this in general, as it adds complexity to your identity resolution strategy. Instead, we recommend having a single, unchanging $user_id for each user and pointing all other IDs for that user to that single $user_id
so I think you'll have to delete the duplicate profiles, and maybe delete and resend the associated events too, depending on your case