Visit the ECR segment of AWS Create a new repository. Keep track of the url.
Log into the the repository using. Note that you may need to install pip install awscli first, and ensure that it's in your shell's PATH variable (mine wasn't on a mac, and I had to enter it into ~/.zshrc)
$ aws ecr get-login --region us-east-1
This will give you the comand that you're wanting to use to authenticate against ECR. However, you're going to have to strip off the -e none https:// bit at the end. The rest should be fine.
Next, you want to see all of your docker images with docker images, and you'll want to tag the one you want to push
$ docker tag cs230 YOUR-AMAZON-USER-ID.dkr.ecr.us-east-1.amazonaws.com/cs230
$ docker push YOUR-AMAZON-USER-ID.dkr.ecr.us-east-1.amazonaws.com/cs230