You get debited a minimum percentage of what is due on your card so that amount varies depending on your monthly spend on the card. You may make ad hoc manual additonal payments via the app. Go to credit card and select "Make payment".
If you want a regular payment set up in addition to the minimum monthly, you can do through setting up a recurring monthly payment to "Standard Bank Card", which can be found under "Pay" and then "Company Search". Recurring payments can be set up for up to 36 months.