Depends on what type of left and right movement... You can do any of the following:
1. Add the platform behavior, then disable the default keys and set your own actions on the key press: On Key Press Left Arrow > Simulate Platform Left
2. You can use the 8 direction movement and do something similar to the above.
3. You can simply add a key press event for the arrow keys or whatever other keys you want and assign them to move the sprites X coordinates + or - depending on the direction.