You don't need to do anything as your merchant or retailer will take payments each month from your chosen card.
Your chosen card will be charged for the first installment straight away. At the same time, an authorization (hold) will be taken for the full outstanding balance to guarantee your plan.
Authorizations for the full outstanding amount of your plan are renewed every 17-21 days or so and reduce with each installment payment made. The previous authorisation is automatically removed as soon as a new one is obtained.
These authorizations may be charged to clear your plan early, if your plan is not kept up to date.
We'll update you on behalf of the merchant or retailer, be keep you posted when monthly installment payments are due/processed and before we attempt to take any authorizations.