From your Admin page, go to Customers > Reward Points, find the customer and click on the "e" icon. Find "Add or Subtract Points" in the new window on the right side, Add or Subtract the desired number of points in the left box and select "Add extra points to Earned" from the drop-down box on the right. Simple, isn't it? (you may select to add the points to Pending or subtract points if you have your own reasons).