You can find Jenkins initial password from EC2 management console System Log.

• Go to Amazon EC2 console at https://console.aws.amazon.com/ec2/.
• Chose your Instance and Click Actions → Instance Settings → Get System log

You can also SSH into your instance and find the login credential using the following command.

$ cat /home/ubuntu/credentials
////////////////////credentials info////////////////////
--- Jenkins
----- User: admin
----- Password : oshei5ha9feelii8AeChaF2Yah3avai5
////////////////////////////////////////////////////////