That’s how I did it, but the process may be different for you. I had a scanerio where our main domain (example.com) was
I have a hostgator hosting, and a domain from PKNIC, I add A record for app.example.com with the Elastic IP of AWS EC2.
Then in IIS, imported the certificate from Server Certificate Menu of IIS.
After that, go to my website, edit the binding and select the certificate I imported for HTTPS protocol. and that’s it.
P.S Hook me up with any questions you have, as I didn’t have time to write a long and well explanatory post.