1. Add Mouse behavior to game
2. Create a new event by double clicking in the event sheet
3. Double click mouse and selecet "On Click" with the green arrow
4. Choose which settings you want
5. Right click your new event and select add new trigger or something like that
6. Double click the sprite in this GUI and find "Compare X"
7. Choose Less Than, and then do Mouse.X
8. To the right of your event there should be some small grey text that says somethin all the lines of add new event with a plus sign
9. In this GUI, select your sprite and find "Set mirrored" choose not mirrored
10. Repeat this with a NEW event (right click > Add new event) but change less than to greather than, and change not mirrored to mirrored
Let me know if anything here is wrong, just woke up and am going off tentop of my head.