You can set this up in just a few minutes from the SoFi mobile app! Once in the app, select "Credit Card" on the Home tab. Select the "Pay" option. At the top of the screen you should see that autopay is off, and an option to "set up". Click "Set up" and follow the prompts to set up your autopay!
Once set up, you should see "Autopay ON: Minimum Amount/Full Account Balance" at the top of your screen. If you would like to make any changes to your autopay you can click the "Manage" button next to the status.