Upload existing ssl cert to acm

I have an existing ssl cert, private key and intermediate certs (obtained using openssl). Not through aws. I want to upload them now using terraform. I found https://github.com/terraform-providers/terraform-provider-aws/issues/3560 that you can upload existing certs. But not able to find an example on how to do this.
there are examples on self service or examples on how one would do this if you let aws manage the whole ssl process but I could not find any example on uploading existing certs obtained through other methods.