Once you have connected a STRIPE account and switched to manual transfers, visit the Transfers tab of Payment Processing for your event.
From here, you will be able initiate transfers (aka payouts) for your event. Enter the amount you would like transferred and a description if you'd like. You can transfer up to the amount you have listed under Remaining on your account.
Note: the numbers on the left under "Event Balance" are specific to the event you are currently viewing. The numbers on the right under "Stripe Account Balance" are for your total balance across events for which you have connected your Stripe account.