Originally, he had one with a servo reverser on it. He just needs to look at his reciever and plug in the second aileron servo into the appropriate channel. No Y harness needed, but maybe a couple of short extensions to make it easier to find the plugs to plug the aileron servos into. I put a piece of tape on the leads and use a magic marker with a L or R on the tape so I plug them in to the correct lead.

"The one I originally installed had like a screw where the leads meet and the "new" one doesn't. Does it need too be programmed into your Tx or how does this then work?"

The screw was a Trimmer Potentiometer (pot) to adjust the throw on the second servo, which is mechanically reversed, to make the throws match from one end of the stick movement to the other.