Below is the usage instruction from AWS marketplace list. Let me know if that helps.
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Usage Instructions: To access FusionPBX, use a browser at
https://<instance public ip address>/. Login is "admin" and password is the EC2 instance ID (e.g., "i-0caff200b36ec4af3"). Please when instances starts for the first time, there is a one-time setup process which may take a few minutes. Please leave sufficient wait time for the first time start-up.
To connect to the operating system, use SSH and the username ec2-user.
As a standard FreeSWITCH configuration, port 5060 is open for authenticated SIP signalling and port 5080 is open for unauthenticated calls (e.g., inbound DID calls).