You've got two ways to disable an Amazon link depending on what you want:
Option 1: Turn it off for a specific post
When you're about to post the video, click the Amazon DM button
It will ask if you want to turn Amazon off for that post
Select yes, and no Amazon link will be sent for that video
Quick walkthrough here:
Option 2: Turn it off globally
Go to your Messages tab
Edit your message templates
Remove the Amazon link placeholder {affiliate_link}
Save
After that, Amazon links won't be sent in your replies anymore.