https://support.plesk.com/hc/en-us/articles/213941265--How-to-change-or-get-the-server-hostname-on-Plesk-server might help. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/set-hostname.html too.
With some clouds (like Google) it can be a pain to persist the changed hostname through reboots, but I think it’s pretty straightforward on AWS - you just change it in Linux/Plesk, and it’ll remember.
The hostname reported in the EC2 console doesn’t really matter - the place you need to change it is inside the operating system and/or Plesk itself.