It's not possible to transfer the funds in your Reward account to your Primary account. This is because your Reward account is meant for you to enjoy in-app purchases and to shop at selected stores, on us!
However, you can transfer funds from your Primary account to your Reward account. Say you want to buy airtime from your Reward account but you're R5.00 short, you can transfer those funds from your Primary account so that you can pay the full amount using your Reward account.
Tak a look at this tutorial for the steps on how to transfer funds between accounts.