Is it possible to turn a specific array element where the initial array is defined as a int, into a character or string?
No, an int array can only hold int values. But note, you can assign 'X' to your int array because a char is an integral type. It won't hold X but it will hold it's numeric value (88).
Tic tac toe. It would need to change the value of squares every time player 1 or player 2 moves, from the integer of the block they selected, to their corresponding symbol (X or O) to mark the block.