The environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY may already have a value. So, check out if values you can see any values if you type these commands.
echo $AWS_SECRET_ACCESS_KEY
echo $AWS_ACCESS_KEY_ID
If yes, then reset these variables using these following commands (if you use aws configure):
unset AWS_ACCESS_KEY_ID
unset AWS_SECRET_ACCESS_KEY
To learn more about AWS, you can check out AWS Tutorial and also enroll for AWS Training.