The process is simple once you understand that you are fetching a public intermediate CA certificate, not a private key. Whether you use the AWS CLI with ACM, directly download from Amazon Trust Services, or extract it from a live load balancer, the steps are reliable and secure.
If you need the M02 certificate file for manual installation or debugging: From the Amazon Trust Repository : Visit the official Amazon Trust Services Repository amazon rsa 2048 m02 certificate download
Why would you ever need to download this certificate? The process is simple once you understand that