I did a factory reset on my RF65A977FB1 and the amazon music app has dissappeard from the installed and available apps.
Before the reset I had a specific app I could search music and play from. Weirdly I can ask Alexa to play a song and it works through amazon music.
Thank!
if you do not get an answer here… you may want to post on the Samsung Community Forum where you may get better support for appliances. I don’t know the solution but do you need to download and install Amazon Music from the screen on the appliance? 
The fridges are quite limited and the app doesn’t appear in the downloadable apps. It’s weird!