Update:
If this answer seems out of place, the original question was "How do i Dulplicate keyframes?"
Probably the easiest way is to the Dope Sheet editor. There are several ways to get there:
- Click the icon on the bottom left corner of the 3D view and select Dope Sheet
- Click on the dropdown that says Default on the Info bar, and select Animation. (Or press CtrlLeft Arrow twice)
This will take you to the Animation layout, with a 3D view, Graph editor, and Dope sheet.
From the Dope sheet or the Graph editor, select keyframes, and press ShiftD to duplicate.
Once you have an animation that ends where it starts, you can make it loop in the Game Engine with Logic Bricks:
Set the end value to the last frame of your animation.