Original matrix:
2 4 5 6 
3 4 6 2
6 7 7 2
1 1 1 1
So after swapping the first and last rows we get:
1 1 1 1
3 4 6 2
6 7 7 2
2 4 5 6

let temp = mxt[0][x]
mxt[0][x] = mxt[size-1][x]
mxt[size-1][x] = temp

import Foundation
import Glibc

// Size of the array 
var size = 3

// Function to interchange the elements
// of first and last rows
func FirstLastInterchange(M:[[Int]]){
   var mxt : [[Int]] = M

   // Interchanging the elements of first
   // and last rows by swapping 
   for x in 0..<size{
      let temp = mxt[0][x]
      mxt[0][x] = mxt[size-1][x]
      mxt[size-1][x] = temp
   }

   // Displaying matrix
   print("Matrix after first and last rows interchange:")
   for m in 0..<size{
      for n in 0..<size{
         print(mxt[m][n], terminator: " ")
      }
      print("\n")
   }
}

// Creating 3x3 matrix of integer type
var myMatrix : [[Int]] = [[11, 33, 44], 
   [55, 66, 77], 
   [88, 33, 22]]

print("Original Matrix:")
for x in 0..<size{
   for y in 0..<size{
      print(myMatrix[x][y], terminator:" ")
   }
   print("\n")
}

// Calling the function 
FirstLastInterchange(M:myMatrix)

Original Matrix:
11 33 44 

55 66 77 

88 33 22 

Matrix after first and last rows interchange:
88 33 22 

55 66 77 

11 33 44