IAM Role Association to the available AWS EC2 instance

As I'm an AWS newbie, I didn't know that I should tag the role while launching the AWS EC2 instance. After launching the AWS EC2 instance, I deployed an application now and get the following error on the console.

com.amazonaws.AmazonServiceException User: arn:aws:iam::XXXXXXXXXXX:user/AWSAdmin is not authorized to perform: sts:AssumeRole on resource: arn:aws:iam::#########:role/myRole

any possiblities to edit the created instance and attach the role to make myApp running? any clue would be much helpful on this. Thanks.