1. Login to the container
docker exec -it registry sh

2. Define variables matching your container and container version:
export NAME="imagename"
export VERSION="imageversion"

3. Move to the the registry directory:
cd /var/lib/registry/docker/registry/v2

4. Delete files related to your hash:
find . | grep `ls ./repositories/$NAME/_manifests/tags/$VERSION/index/sha256`| xargs rm -rf $1

5. Delete manifests:
rm -rf ./repositories/$NAME/_manifests/tags/$VERSION

6. Logout
exit