I\'ve recently gone through the database migration process as outlined here:
https://devcenter.heroku.com/articles/migrating-from-shared-database-to-heroku-postgres<
After deleting the extra rows, you won't get the insert privileges back immediately. In that case, delete the extra rows and just run heroku pg:info
after that. This will refresh the privileges of your DB and you will get the access back in few minutes. Its not required to clone the existing DB into a new one and setting the new one as the DB of your app.
$ heroku pg:info
=== HEROKU_POSTGRESQL_BRONZE_URL, DATABASE_URL
Plan: Hobby-dev
Status: Available
Connections: 3/20
PG Version: 9.3.6
Created: 2014-03-01 13:47 UTC
Data Size: 1.25 GB
Tables: 4
Rows: 2098/10000 (Write access revoked) - refreshing
Fork/Follow: Unsupported
Rollback: Unsupported
Add-on: grinning-busily-5587