AWS Server Image SSH Connection

Hi, I am running the AWS AMI of thinger.io.
Now I would like to add some server endpoints and therefore need to access the server via ssh.
I followed the aws instructions (https://docs.aws.amazon.com/en_en/AWSEC2/latest/UserGuide/putty.html) to connect to my server via putty, but I can’t get a connection.
Which username do I have to use to access the AWS instance?