Having trouble returning the index of a letter in 2D array

I'm trying to find the first occurrence of a user-inputted character in a 2d array. If the character does not exist in the array, the program will return -1. If it does the index will be returned. Can't figure out how to initialize my index, nor do I know how to set the inputted letter to the element within the array. import java.util.Scanner;

public class characterSearch {

public static void main(String[] args) {
    char[][] search = makeArray();

}

public static char[][] makeArray()  {
    Scanner sc = new Scanner(System.in);
    System.out.print("Enter the number of rows: ");
    int numRows = sc.nextInt();
    System.out.print("Enter the number of columns: ");
    int numColumns = sc.nextInt();

    char[][] array = new char[numRows][numColumns];

    System.out.println("Enter " + array.length + " rows and " + array[0].length + " columns");

    for (int row = 0; row < array.length; row++)
        for (int column = 0; column < array[0].length; column++)
            array[row][column] = (char)(Math.random() * (122 - 97) + 97);
    return array;

}

public static int findLetter(char[][] a) {
    Scanner in = new Scanner(System.in);
    System.out.print("Enter a character: ");
    char letter = in.next().charAt(0);
    int index = letter.indexOf(a.length);
    for (int i = 0; i < a.length; i++) {
        if (a[i] = letter) {
            return i;
        }
    }
    return -1;
}

}