You don't adjust the cables at the shifter end...but at the trans end. There's a tool that you're supposed to use that holds the shifter in neutral and centered...but you can get by with a buddy holding it in that position.
Place the car in neutral and have buddy hold shifter centered as best as possible
Go under the car (properly with ramps/jack stands and block behind rear tire)
Locate the cable ends where they attach to the trans
Pull (I believe) the orange lock tabs out (but don't remove), which allows the cable to move back and forth (as you release the orange clip, there may be some slight movement)
With the shifter centered, the trans in neutral, and the orange lock clips released, move the cable end back and forth a bit until you are satisfied that its not under tension (pushing or pulling on the lever) while the trans is in neutral and shifter centered
Once satisfied, push the orange lock clip back on all the way
Done
If either attachment to the trans is missing the bushing the slides onto the arm (common), you'll need to come back on here and search for remedies.