Planet T5 - Fitting The Self Centering Throttle Kit
Sadly most transmitters do not make it particular easy to switch the throttle function to self centering. I can only guess that based on volume sales, only a small percentage of owners want self centering throttles.
So for those that want it, we have to work for it! A number of retail outlets make the parts available from JP (Part # 7710299), which consists of a spring, screw, and two plastic mouldings.
Fitting the parts isn't technically complex, however it can prove a little tricky.