Question about Disney+

Current Events

So my mom has Disney+ year long subscription with a credit card. It's set to renew 2/19.
She wants to renew using the deal which basically gives you 2 months of free D+. I know some of you here do this, so how do I go about doing this?
Just cancel the subscription? And then renew using that deal? Or do I need to create a whole new account using a different email?