1996 Nissan Sentra Stuck in Park

Climbed under the dash to check out brake switch.
Bought a new one at Checkers
-What is the easiest way to loosen and tighten the locknut?
-There is a switch above it. Any idea what that is?
-There was broken black plastic on the floormat. I think that plastic plugs decomposed and fell out of the brake pedal assembly. There are now 2 holes where the switches would contact the pedal assembly. I assume Checkers won't have that and I will have to go to nissan?

Mahalo for the help so far. I really appreciate it!

Our sentra is not stuck in park in fact we went on a nice ride and everything worked well.
The solution cost a total of $2.08 Big Mahalo to Windward Nissan helpful on the phone and in person.

-The $2.08 purchased 2 bright green clear plugs that fit on the shaft of the brake pedal.
-It was incredibly uncomfortable and unpleasant to get down there and get those plugs into the 2 holes, I would suggest buying lunch and beer for a small strong contortionist friend.
-I suggest at least taking off the bottom plastic panel below the steering wheel. It is held on by 2 screws. I don't think taking anything else off helps
-I was most successful loosening and tightening the the locknut with a crowsfoot (14mm) with an extension.
-the switch above the brakelight switch is for the cruise control.

-It was stuck in park because the brakelight switch needs to be "on" to unlock the shift lock. Once the green pad was in and the switch was screwed in properly everything worked great.

On a side note having the brakelights unknowingly on for so long killed our battery, $56 at costco and I replaced the brakelight switch because I assumed that was the problem ($16.00 more).

If I was smart I could have spent $2 instead of $75. It goes to show that you need to check the simple things first: like fuses, plugs, fuel tank not empty, etc.