the end of my shifter broke off which controlles my overdrive, i was wondering how to replace the shifter

 

As I recall, I think it is just pinned in there. Drive out the pin, pull out the shifter.

Before doing that though..... disconnect the switch connector, wherever it happens to end up at..... and tie a string to the end that goes up to the shifter. As you pull the wire out with the shifter, the string will get pulled up as well. When you want to install the new one, tie the string to the wire on the new one, and use it to pull the wire down into place.