To manually add funds to a Customers Wallet, from the Dashboard click Customers.
Click View next to the desired Customer.
Select Wallet from the menu on the left.
Click Top up Wallet.
Enter the desired credit amount.
You can choose to Email a Notification to the Customer regarding the change to their Wallet amount.
Click Add Credit.
(See Wallets: Enabling Wallets for information on how to setup Wallets.)