Admin can add or assign Rewards manually to a customer from the admin end as follows,

 

Click on the Customer and the Reward/Product customer from the left side menus

 

 

Click on Action (dots) and then Assign Reward as shown in the image below,

 

 

Assign Rewards by enabling the check box and click on the Save button once done with the assigning rewards

 

 

Once a reward has been assigned to a user then it cannot be assigned to the same customer again

 

Admin can see the new reward assigned to the customer inside the View Reward section as shown in the image below