How to reset high idle on a 2002 nissan altima 2.5 engine

Without the proper scan/access computer, that is easier said than done.
However, there are some things you can look for... Inspect for possible vacuum leaks that would allow unmetered air into the intake. Check all the fuses. Look also for loose/poor connections at the throttle position sensor and the throttle control actuator/motor, etc.
If you don't find anything obvious, the relearning closed throttle position will require a scan tool and vehicle knowledge.