There are no "reset" buttons
There are no buttons to push on the factory radio to "reset" it. I think you are looking for the Rear Seat Control enable, which I posted under your other question about your rear speakers and headphones.
Disconnecting the battery on your Explorer may cause your radio stations to reset, depending upon the model year and the radio model. Older model radios will default to a set of factory preset radio stations, that were often stations local to the assembly plant building the vehicle. Newer models, with Premium level or Audiophile level radios, as 96EEB said, will maintain the last "user-set" radio presets, regardless of how long the battery power is interrupted.
I hope my explanations have been helpful.
regards,
cobrajeff