You can still access and manage features of your Zip account while it is locked.
From the home screen of the Zip app, click the right-hand side of the product tile you want to manage:
From there, you can continue to manage repayments as normal, such as repay extra and edit your scheduled repayments.
Additionally, you can access your settings via the cog wheel in the top right corner, allowing you to update your payment method, view your statements, and access your contract.