If you're on the Starter plan, you will need to upgrade to our Pro plan or above.
For more details on our plans, take a look at our pricing page. To update your plan, go to the Billing section of your Dashboard: https://builder.knack.com/#billing.
If you're on the Pro plan or above and the "Powered by Knack" is still displaying for your apps, then email us at support@knack.com or send us an in-app message and we'll get that fixed for you!