Yes, it's definitely possible to create payouts/payments for one specific affiliate. However, the way to go about this will depend on whether you're using the Payouts page or the Payments page.
Below you will find two scenarios, with instructions on how you'd conduct a payment/payout for one affiliate.
Scenario 1: You're using the Payouts Page
You can pay out an affiliate from your affiliate's profile.
Go to the left-hand icon 'Affiliates' > Click on the affiliate you intend to payout > Go to Full Profile > Scroll down > Click on 'Generate payout'.
Scenario 2: You're using the Payments Page
All you have to do is click on the "Settle Balance" button next to the affiliate whose balance you wish to settle.
This will open a pop up where you can set the amount you'd like to pay that affiliate and download the payment file.