To manually add credits to a user, simply click on the tab 'Users Balances'.
Once on the 'Users Balances', you can select the user you want to add credits to him.
1. Check the box for the appropriate user
2. Click the 'Edit' button
You just need to change the field value of your money and submit the form.
Note: If the user you want to select is not in the list, you can create it by clicking the 'New' button.